Prevalence of chronic kidney disease stages 3-5 in low- and middle-income countries in Asia: A systematic review and meta-analysis

Chronic kidney disease (CKD) is a major public health problem in low- and middle-income countries (LMICs). Although CKD prevalence has been rapidly increasing in LMICs, particularly in Asia, quantitative studies on the current epidemiology of CKD in this region are limited. This study aimed to identify the prevalence of CKD stages 3-5 in LMICs in Asia, by subregion, country economy classification, identification of CKD, traditional and non-traditional risk factors. A systematic review and meta-analysis of observational studies was conducted through a literature search of seven electronic databases and grey literature search published until November 2021. The Newcastle-Ottawa quality assessment scale (NOS) was used to assess the risk of bias of each study. A random-effects model was used to estimate pooled prevalence. The protocol is registered in the International Prospective Register of Systematic Reviews (PROSPERO CRD42019120519). Of 4,548 potentially relevant records, 110 studies with moderate and high quality were included with 4,760,147 subjects. The average prevalence (95% CI) of CKD stages 3-5 in 14 LMICs in Asia was 11.2% (9.3-13.2%). The prevalence of CKD stages 3-5 was varied among subregions and country economic classification. CKD prevalence was 8.6% (7.2-10.2%) in east Asia, 12.0% (7.7-17.0%) in south-east Asia, 13.1% (8.7-18.2%) in western Asia, and 13.5% (9.5-18.0%) in south Asia. CKD prevalence was 9.8% (8.3-11.5%) in upper-middle-income countries and 13.8% (9.9-18.3%) in lower-middle-income countries. Prevalence of CKD stage 3-5 in LMICs in Asia is comparable to global prevalence. High level of heterogeneity was observed. Study of factors and interventions that lead to the delay of CKD progression is needed.

Medication Adherence, Complementary Medicine Usage and Progression of Diabetic Chronic Kidney Disease in Thais

PURPOSE

Non-adherence to medication is receiving more attention as a significant problem common to management of chronic diseases including diabetes and chronic kidney disease (CKD). This study was designed to assess the medication adherence and self-medication in a cohort of Thai patients with diabetic kidney disease, and its association with clinical outcomes.

PATIENTS AND METHODS

Non-dialysis patients with diabetic CKD visiting outpatient's clinics of Siriraj Hospital, the largest tertiary care in Thailand, were asked for participation. Self-administered questionnaire was given to assess medication adherence (the 6-item-medication-taking-behavior measure in Thai), complementary medicine usage, and personal information. Clinical, pharmaceutical, and relevant laboratory data (at current and the last visit of around 12 months) were abstracted from the medical records.

RESULTS

Of the 220 participants eligible (54.1% male, mean age 71.3), 50.9%, 24.1%, and 25% were classified as high-, medium-, and low-medication adherence, respectively. Overall, 24.1% reported self-usage of at least one type of herbal or complementary medicines. The most commonly identified items were cordyceps, cod liver oil, Nan Fui Chao, and turmeric (6 each), with unidentified Thai herbal mixture in 11. On multivariate analysis, late-stage CKD (stage IV-V) was the only independent predictor for low adherence (odds ratio (OR), 5.54; 95% confidence interval (CI), 2.82-10.88). Low adherence was associated with higher blood pressure, lower estimated glomerular filtrate rate (eGFR), and more eGFR decline with greater risk of being rapid CKD progressor (annual eGFR drop >5 mL/min/1.73 m²) [OR, 1.15; 95% CI, 1.06-1.25].

CONCLUSION

Medication taking behavior was a frequently encountered problem in Thai diabetic CKD patients. Increased medication non-adherence was independently predicted by stages of increasing CKD severity, and it was associated with poorer hypertensive control and kidney outcome. Targeting interventions to improve medication adherence should be an important strategy to slow CKD progression among patients with diabetic CKD.

Testosterone rapidly increases Ca2+-activated K+ currents causing hyperpolarization in human coronary artery endothelial cells

Testosterone has endothelium-dependent vasodilatory effects on the coronary artery, with some reports suggesting endothelial ion channel involvement. This study employed the whole-cell patch clamp technique to investigate the effect of testosterone on ion channels in human coronary artery endothelial cells (HCAECs) and the mechanisms involved. We found that 0.03-3μM testosterone significantly induced a rapid, concentration-dependent increase in total HCAEC current (EC₅₀, 71.96±1.66nM; maximum increase, 59.13±8.37%; mean±SEM). The testosterone-enhanced currents consisted of small- and large-conductance Ca²⁺-activated K⁺ currents (SK_Ca and BK_Ca currents), but not Cl^- and nonselective cation currents. Either a non-permeant testosterone conjugate or the non-aromatizable androgen dihydrotestosterone (DHT) could increase HCAEC currents as well. The androgen receptor antagonist flutamide prevented this testosterone, testosterone conjugate, and DHT effect, while the estrogen receptor antagonist fulvestrant did not. Incubating HCAECs with pertussis toxin or protein kinase A inhibitor H-89 largely inhibited the testosterone effect, while pre-incubation with phospholipase C inhibitor U-73122, prostacyclin inhibitor indomethacin, nitric oxide synthase inhibitor L-NAME or cytochrome P450 inhibitor MS-PPOH, did not. Finally, testosterone application induced HCAEC hyperpolarization within minutes; this effect was prevented by SK_Ca and BK_Ca current inhibitors apamin and iberiotoxin. This is the first electrophysiological demonstration of androgen-induced K_Ca current increase, leading to hyperpolarization, in any endothelial cell, and the first report of SK_Ca as a testosterone target. Our data show that testosterone rapidly increased whole-cell HCAEC SK_Ca and BK_Ca currents via a surface androgen receptor, G_i/o protein, and protein kinase A. This mechanism may explain rapid testosterone-induced coronary vasodilation seen in vivo.

The urea transporter family (SLC14): physiological, pathological and structural aspects

Urea transporters (UTs) belonging to the solute carrier 14 (SLC14) family comprise two genes with a total of eight isoforms in mammals, UT-A1 to -A6 encoded by SLC14A2 and UT-B1 to -B2 encoded by SLC14A1. Recent efforts have been directed toward understanding the molecular and cellular mechanisms involved in the regulation of UTs using transgenic mouse models and heterologous expression systems, leading to important new insights. Urea uptake by UT-A1 and UT-A3 in the kidney inner medullary collecting duct and by UT-B1 in the descending vasa recta for the countercurrent exchange system are chiefly responsible for medullary urea accumulation in the urinary concentration process. Vasopressin, an antidiuretic hormone, regulates UT-A isoforms via the phosphorylation and trafficking of the glycosylated transporters to the plasma membrane that occurs to maintain equilibrium with the exocytosis and ubiquitin-proteasome degradation pathways. UT-B isoforms are also important in several cellular functions, including urea nitrogen salvaging in the colon, nitric oxide pathway modulation in the hippocampus, and the normal cardiac conduction system. In addition, genomic linkage studies have revealed potential additional roles for SLC14A1 and SLC14A2 in hypertension and bladder carcinogenesis. The precise role of UT-A2 and presence of the urea recycling pathway in normal kidney are issues to be further explored. This review provides an update of these advances and their implications for our current understanding of the SLC14 UTs.

Glomerular macrophage is an indicator of early treatment response in diffuse proliferative lupus nephritis

BACKGROUND

Patients with diffuse proliferative lupus nephritis (class IV) who responded to treatment within 6 months had better renal outcome than those who did not. Glomerular macrophage is known to be associated with poor renal outcome in glomerular diseases.

OBJECTIVE

To evaluate association between glomerular macrophage number and early treatment response in lupus nephritis class IV patients.

MATERIAL AND METHOD

Renal biopsies (n = 90, 86 females) diagnosed with lupus nephritis class IV were included in the study. The patients were divided into 2 groups (n = 45 each) according to response to treatment within 6 months. The treatment response group was defined as having decreased serum creatinine at least 25% from baseline and 24 hr urine protein or UPCR (urine protein creatinine ratio) < 1. The non-response group was defined as stable or increased serum creatinine and 24 hr urine protein or UPCR > or = 1. Immunohistochemistry for macrophage marker (CD68) was performed and the glomerular macrophages were counted on each biopsy. The relevant clinicopathologic data were collected.

RESULTS

The glomerular macrophage number in response and non-response group was 4.5 +/- 2.5 and 6.2 +/- 4.5 respectively (p = 0.029). The glomerular macrophage number was conversely and inversely correlated with activity (r = 0.281, p = 0.007) and chronicity (r = -0.358, p < 0.001) index, respectively

CONCLUSION

Lupus nephritis class IV patients who responded to treatment within 6 months had lower glomerular macrophages than those who did not. The glomerular macrophage number may be used to determine treatment response in lupus nephritis class IV patients.

Can we predict final outcome of internal medicine residents with in-training evaluation

OBJECTIVE

To assess the predictive value of in-training evaluation for determining future success in the internal medicine board certifying examination.

MATERIAL AND METHOD

Ninety-seven internal medicine residents from Faculty of Medicine Siriraj Hospital who undertake the Thai Board examination during the academic year 2006-2008 were enrolled. Correlation between the scores during internal medicine rotation and final scores in board examination were then examined.

RESULTS

Significant positive linear correlation was found between scores from both written and clinical parts of board certifying examination and scores from the first-year summative written and clinical examinations and also the second-year formative written examination (r = 0.43-0.68, p < 0.001). Monthly evaluation by attending staffs was less well correlated (r = 0.29-0.36) and the evaluation by nurses or medical students demonstrated inverse relationship (r = -0.2, p = 0.27 and r = -0.13, p = 0.48).

CONCLUSION

Some methods of in-training evaluation can predict successful outcome of board certifying examination. Multisource assessments cannot well extrapolate some aspects of professional competences and qualities.

Immunohistochemical study for the diagnosis of Alport's syndrome

BACKGROUND

Alport's syndrome (AS) is the most common cause of inherited glomerular disease in Thailand. The majority of cases show X-linked inheritance, which is caused by mutations in the gene coding for the alpha5 chain of type IV collagen in the glomerular basement membrane (GBM) and epidermal basement membrane (EBM). Such mutation usually leads to a reduction in protein amount, thus, immunohistochemical studies have been considered in diagnostic evaluation.

OBJECTIVE

To study the expression of alpha[IV] collagen chains in the skin as an alternative approach to diagnose AS.

MATERIAL AND METHOD

Eleven unrelated probands with proven AS, 7 relatives with abnormal urinalysis, 4 suspected individuals, and 8 normal controls were enrolled. A punch skin biopsy and immunofluorescence staining of the tissue specimens for alpha1, alpha3 and alpha5[IV] collagen chains was performed.

RESULTS

The alpha5[IV] chain was absent in the EBM in all male AS patients while a discontinuing pattern was observed in all females except one. The findings are specific for AS with a sensitivity of 91%. Studies in relatives and suspected individuals also confirmed the advantage of this approach as demonstrated by the absence and discontinuation of alpha5[IV] staining in all males and females, respectively. We also analyzed their expressions in the kidney tissue and demonstrated abnormal alpha3 and alpha5[IV] staining in five of six samples.

CONCLUSION

Immunohistochemical study of the skin should be used as a screening method in patients suspected of AS, as it is much less invasive. Moreover, it is a useful adjunct to conventional examination of biopsied renal tissue.

Effect of short-term folate and vitamin B supplementation on blood homocysteine level and carotid artery wall thickness in chronic hemodialysis patients

OBJECTIVE

Hyperhomocysteinemia is an independent risk factor for atherosclerotic vascular disease in chronic hemodialysis patients. This stratified randomized controlled trial was designed to measure the effect of high dose oral vitamin B6, vitamin B12, and folic acid on homocysteine levels, and to evaluate the effect on atherosclerosis as measured by Intima-Media Thickness (IMT) of carotid arteries.

MATERIAL AND METHOD

Fifty-four chronic hemodialysis patients with hyperhomocysteinemia were randomized to receive oral 15 mg folic acid, 50 mg vitamin B6, and 1 mg vitamin B12 daily (treatment group) or oral 5 mg folic acid alone (control group) for 6 months. Homocysteine level and IMT were measured in both groups.

RESULTS

At 6 months, homocysteine levels in the treatment group were significantly reduced from 27.94 +/- 8.54 to 22.71 +/- 3.68 mmol/l (p = 0.009) and were not significantly increased from 26.81 +/- 7.10 to 30.82 +/- 8.76 mmol/l in control group (p = 0.08). Mean difference between both groups was statistically significant (p = 0.002). There was no significant difference of IMT of carotid arteries, however, a tendency that the treatment group would have less thickness was observed (0.69 +/- 0.29 mm and 0.62 +/- 0.16 mm, p = 0.99).

CONCLUSION

Treatment of hyperhomocysteinemia in chronic hemodialysis patients with daily oral 15 mg folic acid, 50 mg vitamin B6, and 1 mg vitamin B12 for 6 months decreases homocysteine levels and tends to reduce IMT of carotid arteries. A long term study for the prevention of atherosclerosis is warranted.

An analysis of 3,555 cases of renal biopsy in Thailand

BACKGROUND

The knowledge of the epidemiology of biopsied renal diseases provides useful information in clinical practice. There are several epidemiologic population-based studies of biopsy-proven nephropathies with detailed clinicopathologic correlations that could be different according to the country analyzed.

OBJECTIVE

To identify the prevalence of primary and secondary glomerular diseases and to study the trend of the pattern changes of the glomerulopathy in Thailand.

MATERIAL AND METHOD

A retrospective study of percutaneous renal biopsies during a 23-year period of 1982 to 2005 was performed. A total of 3,555 consecutive native kidney biopsies in adult patients between 12 and 84 years of age were analyzed for the prevalence and changes in the 5-year interval over the two decades.

RESULTS

From the clinical trial of 3,275 patients, the ratio between primary and secondary glomerular diseases was 2:1 (2154:1121). The most common primary glomerular disease (2154 patients) were IgM nephropathy (n = 986, 45.8%) followed by IgA nephropathy (n = 386, 17.9%); membranous nephropathy (n = 341, 15.8%); diffuse endocapillary proliferative glomerulonephritis (n = 114, 5.3%) and diffuse crescentic glomerulonephritis (n = 71, 3.3%). Lupus nephritis was the most prevalent cause of secondary glomerulonephritis in the present study (n = 992, 88.5%). Examination of the 5-year interval along the study period revealed a significant increase in the prevalence of IgA nephropathy and diabetic nephropathy. Prevalence of focal and segmental glomerulosclerosis rose by five times over the last two decades in contrast to IgM nephropathy, which prevalence is decreasing.

CONCLUSION

There is high prevalence of IgM nephropathy, IgA nephropathy, and lupus nephritis in Thailand which is different from other countries. It could be due to various races and altered environments. The information obtained from these results is an important contribution for the understanding of the prevalence in renal diseases in Thailand. It can be used as the baseline data for making efficient research into the appropriate and beneficial way of management in the future.

Abnormal kinetics of erythrocyte sodium lithium countertransport in patients with diabetic nephropathy in Thailand

BACKGROUND

In essential hypertension and diabetic nephropathy, sodium-lithium counter transport (Na/Li CT) is an inherited marker for metabolic influences of cardiovascular risk. The kinetics of Na/Li CT are modified by two types of thiol group in the membrane. In choline medium, the type 1 thiol reacts with N-ethtyl maleimide (NEM) to cause a decrease in Km and increase Vmax/Km ratio. However in the presence of external Na or Li both the type 1 or type 2 thiols react so that both Km and Vmax are reduced. Low Km of Na/Li CT has been previously reported to be a major abnormality in diabetic nephropathy (DN) and can be used to identify diabetic patients who are at high risk for DN. A recent study showed that the type 1 thiol protein controlling the Km of Na/Li CT was a 33-kD protein and the gene for this protein is going to be cloned.

OBJECTIVE

The authors sought to identify Na/Li CT kinetic abnormalities in Type 2 diabetes in Thai patients.

MATERIAL AND METHOD

Erythrocyte Na/Li CT kinetics and their modulation by thiol proteins were measured in erythrocytes from 22 patients with Type 2 diabetes and 42 normal control subjects.

RESULTS

The kinetics of Na/Li CT in untreated erythrocytes were similar Thiol protein alkylation with NEM generally caused both Vmax and Km to fall, but caused Km to rise in erythrocytes of diabetic patients, whose native Km was low. Thus, abnormalities in the regulation of Na/Li CT by key thiol proteins were found in about one-third of subjects with Type 2 diabetes in Thailand.

CONCLUSION

Membrane abnormalities may indicate a common pathway of pathological mechanism found in essential hypertension and diabetic nephropathy and may be used as a phenotype for further genetic studies of this transporter.

Relationship between hyperhomocysteinemia and atherosclerosis in chronic hemodialysis patients

BACKGROUND

Hyperhomocysteinemia is an independent risk factor of coronary artery heart disease (CAHD) and atherosclerosis in a normal population. However, it is still controversial in end-stage kidney disease patients who underwent long-term dialysis. Carotid intima-media thickness (IMT) is the standard non-invasive measurement of atherosclerosis. The aims of the present study were to determine the homocysteine (Hcy) level, and to evaluate its role as a risk factor of atherosclerosis in hemodialysis (HD) patients.

MATERIAL AND METHOD

Clinical data and blood chemistries were assayed in 62 HD patients. Atherosclerosis was defined by clinical presentations of CAHD, cerebrovascular or peripheral vascular diseases, or carotid plaque by ultrasound. IMT was also measured by ultrasound

RESULTS

Plasma Hcy level in HD patients was significantly higher in HD patients than normal controls (28.3 +/- 8.3 vs 9.7 +/- 2.9 micromol/l, p < 0.001). Older age (p < 0.001), male sex (p = 0.05), longer duration of HD (p = 0.05), and higher plasma Hcy level (p = 0.01) correlated with atherosclerosis by univariate analysis, but plasma Hcy did not show significant correlation by multivariable analysis. There was also correlation between IMT and atherosclerosis in HD patients (p < 0.001) but no correlation was observed between plasma Hcy level and lMT.

CONCLUSION

Hyperhomocysteinemia is not an independent factor in the genesis of atherosclerosis in HD patients. Advanced age plays a major role of hyperhomocysteinemia and IMT is a useful marker of atherosclerosis in these patients.

Defects in processing and trafficking of the AE1 Cl-/HCO3- exchanger associated with inherited distal renal tubular acidosis

Distal renal tubular acidosis (dRTA) results from impaired urinary acidification by the renal collecting duct. Acquired dRTA can be secondary to diverse pathological processes, including diabetic, ischemic, fibrosing, or immunological processes; less frequently it presents as a familial disorder with either an autosomal recessive or dominant pattern of transmission. Mutations in the SLC4A1/AE1/band 3 Cl(-)/HCO(3)(-) exchanger gene have been identified as causes for both dominant and recessive forms of dRTA. These mutations comprise a group almost entirely distinct from the SLC4A1 mutations that underlie the familial hemolytic anemia of hereditary spherocytosis. Why does one group of mutations express almost exclusively an isolated erythroid phenotype, whereas the second group of mutations expresses almost exclusively a phenotype explicable entirely by defective function of renal collecting duct type A intercalated cells? This review summarizes current research addressing this central question in the pathobiology of inherited dRTA associated with mutations in the SLC4A1 gene. Studying dRTA-associated mutant AE1 polypeptides can provide novel insights into the biology of the intercalated cell and the collecting duct as well as more generally into mechanisms by which epithelial cells generate and maintain functional polarity.

Characterization of a highly polymorphic marker adjacent to the SLC4A1 gene and of kidney immunostaining in a family with distal renal tubular acidosis

BACKGROUND

Mutations in the human SLC4A1 (AE1/band 3) gene are associated with hereditary spherocytic anaemia and with distal renal tubular acidosis (dRTA). The molecular diagnosis of AE1 mutations has been complicated by the absence of highly polymorphic genetic markers, and the pathogenic mechanisms of some dRTA-associated AE1 mutations remain unclear. Here, we characterized a polymorphic dinucleotide repeat close to the human AE1 gene and performed an immunocytochemical study of kidney tissue from a patient with inherited dRTA with a defined AE1 mutation.

METHODS

One CA repeat region was identified in a phage P1-derived artificial chromosome (PAC) clone containing most of the human AE1 gene and the upstream flanking region. We determined its heterozygosity value in multiple populations by PCR analysis. Genotyping of one family with dominant dRTA identified the AE1 R589H mutation, and family member genotypes were compared with the CA repeat length. AE1 and vH(+)-ATPase polypeptides in kidney tissue from an AE1 R589H patient were examined by immunocytochemistry for the first time.

RESULTS

This CA repeat, previously reported as D17S1183, is approximately 90 kb upstream of the AE1 gene and displayed considerable length polymorphism, with small racial differences, and a heterozygosity value of 0.56. The allele-specific length of this repeat confirmed co-segregation of the AE1 R589H mutation with the disease phenotype in a family with dominant dRTA. Immunostaining of the kidney cortex from one affected member with superimposed chronic pyelonephritis revealed vH(+)-ATPase-positive intercalated cells in which AE1 was undetectable, and proximal tubular epithelial cells with apparently enhanced apical vH(+)-ATPase staining.

CONCLUSIONS

The highly polymorphic dinucleotide repeat adjacent to the human AE1 gene may be useful for future studies of disease association and haplotype analysis. Intercalated cells persist in the end-stage kidney of a patient with familial autosomal dominant dRTA associated with the AE1 R589H mutation. The absence of detectable AE1 polypeptide in those intercalated cells supports the genetic prediction that the AE1 R589H mutation indeed causes dominant dRTA.

The SLC14 gene family of urea transporters

Carrier-mediated urea transport allows rapid urea movement across the cell membrane, which is particularly important in the process of urinary concentration and for rapid urea equilibrium in non-renal tissues. Urea transporters mediate passive urea uptake that is inhibited by phloretin and urea analogues. Facilitated urea transporters are divided into two classes: (1) the renal tubular/testicular type of urea transporter, UT-A1 to -A5, encoded by alternative splicing of the SLC14A2 gene, and (2) the erythrocyte urea transporter UT-B1 encoded by the SLC14A1 gene. The primary structure of urea transporters is unique, consisting of two extended, hydrophobic, membrane-spanning domains and an extracellular glycosylated-connecting loop. UT-A1 is the result of a gene duplication of this two-halves-structure, and the duplicated portions are linked together by a large intracellular hydrophilic loop, carrying several putative protein kinase A (PKA) and -C (PKC) phosphorylation sites. UT-A1 is located in the apical membrane of the kidney inner medullary collecting duct cells, where it is stimulated acutely by cAMP-mediated phosphorylation in response to the antidiuretic hormone vasopressin. Vasopressin also up-regulates UT-A2 mRNA/protein expression in the descending thin limb of the loops of Henle. UT-A1 and UT-A2 are regulated independently and respond differently to changes in dietary protein content. UT-A3 and UT-A4 are located in the rat kidney medulla and UT-A5 in the mouse testis. The widely expressed UT-B participates in urea recycling in the descending vasa recta, as demonstrated by a relatively mild "urea-selective" urinary concentrating defect in transgenic UT-B null mice and individuals with the Jk(null) blood group.

Molecular characterization of a novel urea transporter from kidney inner medullary collecting ducts

In the terminal part of the kidney collecting duct, rapid urea reabsorption is essential to maintaining medullary hypertonicity, allowing maximal urinary concentration to occur. This process is mediated by facilitated urea transporters on both apical and basolateral membranes. Our previous studies have identified three rat urea transporters involved in the urinary concentrating mechanism, UT1, UT2 and UT3, herein renamed UrT1-A, UrT1-B, and UrT2, which exhibit distinct spatial distribution in the kidney. Here we report the molecular characterization of an additional urea transporter isoform, UrT1-C, from rat kidney that encodes a 460-amino acid residue protein. UrT1-C has 70 and 62% amino acid identity to rat UrT1-B and UrT2 (UT3), respectively, and 99% identity to a recently reported rat isoform (UT-A3; Karakashian A, Timmer RT, Klein JD, Gunn RB, Sands JM, and Bagnasco SM. J Am Soc Nephrol 10: 230-237, 1999). We report the anatomic distribution of UrT1-C in the rat kidney tubule system as well as a detailed functional characterization. UrT1-C m RNA is primarily expressed in the deep part of the inner medulla. When expressed in Xenopus laevis oocytes, UrT1-C induced a 15-fold stimulation of urea uptake, which was inhibited almost completely by phloretin (0.7 mM) and 60-95% by thiourea analogs (150 mM). The characteristics are consistent with those described in perfusion studies with inner medullary collecting duct (IMCD) segments, but, contrary to UrT1-A, UrT1-C-mediated urea uptake was not stimulated by activation of protein kinase A. Our data show that UrT1-C is a phloretin-inhibitable urea transporter expressed in the terminal collecting duct that likely serves as an exit mechanism for urea at the basolateral membrane of IMCD cells.

Inherited renal tubular acidosis

The past few years have witnessed great progress in elucidating the molecular basis of inherited renal tubular acidosis. Consistent with the physiologically defined importance of multiple gene products in urinary acidification, heritable renal tubular acidosis is genetically heterogeneous. Autosomal dominant distal renal tubular acidosis has been associated with a small number of mutations in the AE1 Cl-/HCO3- exchanger although the pathophysiologic mechanisms behind these mutations remain unclear. Rarely, autosomal recessive distal RTA is caused by homozygosity or compound heterozygosity for the loss-of-function mutation AE1 G701D. A larger proportion, often accompanied by hearing loss, is associated with mutations in the ATP6B1 gene encoding the 58 kDa B1 subunit of the vacuolar H+-ATPase. Mutations in the gene encoding the Na+/HCO3- cotransporter, NBC1, have recently been identified in proximal renal tubular acidosis with corneal calcification.

Long-term regulation of urea transporter expression by vasopressin in Brattleboro rats

Regulation of urea concentration in the renal medullary interstitium is important for maintenance of hypertonicity and therefore the osmotic driving force for water reabsorption. Studies in Sprague-Dawley rats showed that restriction of water intake for 3 days results in upregulation of urea transporter (UT) mRNA in the inner stripe of outer medulla of the kidney (2.9-kb UT2) but not in the inner medulla (4.0-kb UT1). The present study was performed to investigate the role of vasopressin in long-term regulation of UT1 and UT2 in neurogenic diabetes insipidus (Brattleboro) rats treated with a 7-day continuous infusion of [Arg(8)]-vasopressin (AVP), [deamino-Cys(1), D-Arg(8)]-vasopressin (dDAVP) or vehicle. Northern analysis showed that water restriction alone had no effect on the level of UT2 mRNA in vehicle-treated Brattleboro rats but UT2 mRNA markedly increased and UT1 mRNA modestly decreased after treatment with dDAVP. In situ hybridization further demonstrated that the UT2 signal is upregulated and spread along the descending thin limbs of loops of Henle and that UT1 signal is downregulated in the inner medullary collecting ducts in vasopressin-treated rats, with a greater response for dDAVP compared with the AVP-treated group. Immunocytochemistry studies revealed that the UT1 and UT2 proteins are also modified in the same pattern as the transcript changes. Our studies reveal the role of vasopressin in long-term regulation of UT1 and UT2 expression during water restriction.

Novel AE1 mutations in recessive distal renal tubular acidosis. Loss-of-function is rescued by glycophorin A

The AE1 gene encodes band 3 Cl-/HCO3- exchangers that are expressed both in the erythrocyte and in the acid-secreting, type A intercalated cells of the kidney. Kidney AE1 contributes to urinary acidification by providing the major exit route for HCO3- across the basolateral membrane. Several AE1 mutations cosegregate with dominantly transmitted nonsyndromic renal tubular acidosis (dRTA). However, the modest degree of in vitro hypofunction exhibited by these dRTA-associated mutations fails to explain the disease phenotype in light of the normal urinary acidification associated with the complete loss-of-function exhibited by AE1 mutations linked to dominant spherocytosis. We report here novel AE1 mutations linked to a recessive syndrome of dRTA and hemolytic anemia in which red cell anion transport is normal. Both affected individuals were triply homozygous for two benign mutations M31T and K56E and for the loss-of-function mutation, G701D. AE1 G701D loss-of-function was accompanied by impaired trafficking to the Xenopus oocyte surface. Coexpression with AE1 G701D of the erythroid AE1 chaperonin, glycophorin A, rescued both AE1-mediated Cl- transport and AE1 surface expression in oocytes. The genetic and functional data both suggest that the homozygous AE1 G701D mutation causes recessively transmitted dRTA in this kindred with apparently normal erythroid anion transport.

Molecular characterization of a broad selectivity neutral solute channel

In all living cells, coordination of solute and water movement across cell membranes is of critical importance for osmotic balance. The current concept is that these processes are of distinct biophysical nature. Here we report the expression cloning of a liver cDNA encoding a unique promiscuous solute channel (AQP9) that confers high permeability for both solutes and water. AQP9 mediates passage of a wide variety of non-charged solutes including carbamides, polyols, purines, and pyrimidines in a phloretin- and mercury-sensitive manner, whereas amino acids, cyclic sugars, Na+, K+, Cl-, and deprotonated monocarboxylates are excluded. The properties of AQP9 define a new evolutionary branch of the major intrinsic protein family of aquaporin proteins and describe a previously unknown mechanism by which a large variety of solutes and water can pass through a single pore, enabling rapid cellular uptake or exit of metabolites with minimal osmotic perturbation.

Urea transporters in kidney: molecular analysis and contribution to the urinary concentrating process1

Facilitated urea transporters (UTs) are responsible for urea accumulation in the renal inner medulla of the mammalian kidney and therefore play a central role in the urinary concentrating process. Recently, the cDNAs encoding three members of the UT family, UT1, UT2, and UT3 have been cloned. These transporters are expressed in different structures of the mammalian kidney. In rat, UT1 resides in the apical membrane of terminal inner medullary collecting ducts, where it mediates vasopressin-regulated urea reabsorption. UT2 and UT3 are located in descending thin limbs of Henle's loop and descending vasa recta, respectively, and participate in urinary recycling processes, which minimize urea escape from the inner medulla. UT1 and UT2 are regulated independently and respond differently to changes in dietary protein content and hydration state. Identification and characterization of these urea transporters advances our understanding of the molecular basis and regulation of the urinary concentrating mechanism.

Characterization of a rat Na+-dicarboxylate cotransporter

The metabolism of Krebs cycle intermediates is of fundamental importance for eukaryotic cells. In the kidney, these intermediates are transported actively into epithelial cells. Because citrate is a potent inhibitor for calcium stone formation, excessive uptake results in nephrolithiasis due to hypocitraturia. We report the cloning and characterization of a rat kidney dicarboxylate transporter (SDCT1). In situ hybridization revealed that SDCT1 mRNA is localized in S3 segments of kidney proximal tubules and in enterocytes lining the intestinal villi. Signals were also detected in lung bronchioli, the epididymis, and liver. When expressed in Xenopus oocytes, SDCT1 mediated electrogenic, sodium-dependent transport of most Krebs cycle intermediates (Km = 20-60 microM), including citrate, succinate, alpha-ketoglutarate, and oxaloacetate. Of note, the acidic amino acids L- and D-glutamate and aspartate were also transported, although with lower affinity (Km = 2-18 mM). Transport of citrate was pH-sensitive. At pH 7.5, the Km for citrate was high (0.64 mM), whereas at pH 5.5, the Km was low (57 microM). This is consistent with the concept that the -2 form of citrate is the transported species. In addition, maximal currents at pH 5.5 were 70% higher than those at pH 7.5, and our data show that the -3 form acts as a competitive inhibitor. Simultaneous measurements of substrate-evoked currents and tracer uptakes under voltage-clamp condition, as well as a thermodynamic approach, gave a Na+ to citrate or a Na+ to succinate stoichiometry of 3 to 1. SDCT1-mediated currents were inhibited by phloretin. This plant glycoside also inhibited the SDCT1-specific sodium leak in the absence of substrate, indicating that at least one Na+ binds to the transporter before the substrate. The data presented provide new insights into the biophysical characteristics and physiological implications of a cloned dicarboxylate transporter.

Cloning and characterization of a potassium-coupled amino acid transporter

Active solute uptake in bacteria, fungi, plants, and animals is known to be mediated by cotransporters that are driven by Na+ or H+ gradients. The present work extends the Na+ and H+ dogma by including the H+ and K+ paradigm. Lepidopteran insect larvae have a high K+ and a low Na+ content, and their midgut cells lack Na+/K+ ATPase. Instead, an H+ translocating, vacuolar-type ATPase generates a voltage of approximately -240 mV across the apical plasma membrane of so-called goblet cells, which drives H+ back into the cells in exchange for K+, resulting in net K+ secretion into the lumen. The resulting inwardly directed K+ electrochemical gradient serves as a driving force for active amino acid uptake into adjacent columnar cells. By using expression cloning with Xenopus laevis oocytes, we have isolated a cDNA that encodes a K+-coupled amino acid transporter (KAAT1). We have cloned this protein from a larval lepidopteran midgut (Manduca sexta) cDNA library. KAAT1 is expressed in absorptive columnar cells of the midgut and in labial glands. When expressed in Xenopus oocytes, KAAT1 induced electrogenic transport of neutral amino acids but excludes alpha-(methylamino)isobutyric acid and charged amino acids resembling the mammalian system B. K+, Na+, and to a lesser extent Li+ were accepted as cotransported ions, but K+ is the principal cation, by far, in living caterpillars. Moreover, uptake was Cl(-)-dependent, and the K+/Na+ selectivity increased with hyperpolarization of oocytes, reflecting the increased K+/Na+ selectivity with hyperpolarization observed in midgut tissue. KAAT1 has 634 amino acid residues with 12 putative membrane spanning domains and shows a low level of identity with members of the Na+ and Cl(-)-coupled neurotransmitter transporter family.

Autosomal dominant distal renal tubular acidosis is associated in three families with heterozygosity for the R589H mutation in the AE1 (band 3) Cl-/HCO3- exchanger

Distal renal tubular acidosis (dRTA) is characterized by defective urinary acidification by the distal nephron. Cl-/HCO3- exchange mediated by the AE1 anion exchanger in the basolateral membrane of type A intercalated cells is thought to be an essential component of lumenal H+ secretion by collecting duct intercalated cells. We evaluated the AE1 gene as a possible candidate gene for familial dRTA. We found in three unrelated families with autosomal dominant dRTA that all clinically affected individuals were heterozygous for a single missense mutation encoding the mutant AE1 polypeptide R589H. Patient red cells showed approximately 20% reduction in sulfate influx of normal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid sensitivity and pH dependence. Recombinant kidney AE1 R589H expressed in Xenopus oocytes showed 20-50% reduction in Cl-/Cl- and Cl-/HCO3- exchange, but did not display a dominant negative phenotype for anion transport when coexpressed with wild-type AE1. One apparently unaffected individual for whom acid-loading data were unavailable also was heterozygous for the mutation. Thus, in contrast to previously described heterozygous loss-of-function mutations in AE1 associated with red cell abnormalities and apparently normal renal acidification, the heterozygous hypomorphic AE1 mutation R589H is associated with dominant dRTA and normal red cells.

Localization of the high-affinity glutamate transporter EAAC1 in rat kidney

Most amino acids filtered by the glomerulus are reabsorbed in the kidney via specialized transport systems. Recently, the cDNA encoding a high-affinity glutamate transporter, EAAC1, has been isolated and shown to be expressed at high levels in the kidney. To determine the potential role of EAAC1 in renal acidic amino acid reabsorption, the distribution of EAAC1 mRNA and protein in rat kidney was examined. In situ hybridization revealed that EAAC1 mRNA is expressed predominantly in S2 and S3 segments of the proximal tubules and at low levels in the inner stripe of outer medulla and inner medulla. Polyclonal antibodies raised against the carboxy terminus of EAAC1 recognized a single band of approximately 70 kDa on Western blots of membrane protein from kidney cortex and medulla. Immunofluorescence microscopy revealed intense signals in the luminal membrane of S2 and S3 segments and weaker signals in S1 segments, descending thin limbs of long-loop nephrons, medullary thick ascending limbs, and distal convoluted tubules. These results are consistent with EAAC1 encoding the previously described apical high-affinity glutamate transporter in the kidney that mediates reabsorption of acidic amino acids in tubules beyond early proximal tubule S1 segments. Potential additional roles of EAAC1 in acid/base balance, cell volume regulation, and amino acid metabolism are discussed.

Segmental localization of urea transporter mRNAs in rat kidney

Renal epithelia express at least two distinct urea transporter mRNAs, termed UT1 and UT2, that are derived from a single UT gene by alternative splicing. Previous immunolocalization studies using a polyclonal antibody that does not distinguish between the protein products of these two transcripts revealed that expression of urea transporter protein is restricted to inner medullary collecting ducts and descending thin limbs of Henle's loop. To identify which transcripts account for protein expression in these two structures, we carried out reverse transcription-polymerase chain reaction studies in microdissected structures using UT1- and UT2-specific primers. UT1 mRNA was detected only in the inner medullary collecting duct, consistent with its identification as the vasopressin-regulated urea transporter. In contrast, UT2-mRNA was detected in the late part of descending thin limbs of short loops of Henle and in the inner medullary part of descending thin limbs of long loops of Henle. This localization is consistent with the predicted role of UT2 in medullary urea recycling. Thus, in conjunction with foregoing physiological studies, our data indicate that these transporters play central roles in the urinary concentrating mechanism.

Cloning and characterization of the urea transporter UT3: localization in rat kidney and testis

Urea transport in the kidney plays an important role in urinary concentration and nitrogen balance. Recently, three types of urea transporters have been cloned, UT1 and UT2 from rat and rabbit kidney and HUT11 from human bone marrow. To elucidate the physiological role of the latter urea transporter, we have isolated the rat homologue (UT3) of HUT11 and studied its distribution of expression and functional characteristics. UT3 cDNA encodes a 384 amino acid residue protein, which has 80% identity to the human HUT11 and 62% identity to rat UT2. Functional expression in Xenopus oocytes induced a large (approximately 50-fold) increase in the uptake of urea compared with water-injected oocytes. The uptake was inhibited by phloretin (0.75 mM) and pCMBS (0.5 mM) (55 and 32% inhibition, respectively). Northern analysis gave a single band of 3.8 kb in kidney inner and outer medulla, testis, brain, bone marrow, spleen, thymus, and lung. In situ hybridization of rat kidney revealed that UT3 mRNA is expressed in the inner stripe of the outer medulla, inner medulla, the papillary surface epithelium, and the transitional urinary epithelium of urinary tracts. Co-staining experiments using antibody against von Willebrand factor showed that UT3 mRNA in the inner stripe of the outer medulla is expressed in descending vasa recta. These data suggest that UT3 in kidney is involved in counter current exchange between ascending and descending vasa recta, to enhance the cortico-papillary osmolality gradient. In situ hybridization of testis revealed that UT3 is located in Sertoli cells of seminiferous tubules. The signal was only detected in Sertoli cells associated with the early stages of spermatocyte development, suggesting that urea may play a role in spermatogenesis.

Molecular characteristics of mammalian and insect amino acid transporters: implications for amino acid homeostasis

In mammalian cells, the uptake of amino acids is mediated by specialized, energy-dependent and passive transporters with overlapping substrate specificities. Most energy-dependent transporters are coupled either to the cotransport of Na+ or Cl- or to the countertransport of K+. Passive transporters are either facilitated transporters or channels. As a prelude to the molecular characterization of the different classes of transporters, we have isolated transporter cDNAs by expression-cloning with Xenopus laevis oocytes and we have characterized the cloned transporters functionally by uptake studies into oocytes using radiolabelled substrates and by electrophysiology to determine substrate-evoked currents. Mammalian transporters investigated include the dibasic and neutral amino acid transport protein D2/NBAT (system b0+) and the Na(+)- and K(+)-dependent neuronal and epithelial high-affinity glutamate transporter EAAC1 (system XAG-). A detailed characterization of these proteins has provided new information on transport characteristics and mechanisms for coupling to different inorganic ions. This work has furthermore advanced our understanding of the roles these transporters play in amino acid homeostasis and in various pathologies. For example, in the central nervous system, glutamate transporters are critically important in maintaining the extracellular glutamate concentration below neurotoxic levels, and defects of the human D2 gene have been shown to account for the formation of kidney stones in patients with cystinuria. Using similar approaches, we are investigating the molecular characteristics of K(+)-coupled amino acid transporters in the larval lepidopteran insect midgut. In the larval midgut, K+ is actively secreted into the lumen through the concerted action of an apical H+ V-ATPase and an apical K+/2H+ antiporter, thereby providing the driving force for absorption of amino acids. In vivo, the uptake occurs at extremely high pH (pH 10) and is driven by a large potential difference (approximately -200 mV). Studies with brush-border membrane vesicles have shown that there are several transport systems in the larval intestine with distinct amino acid and cation specificities. In addition to K+, Na+ can also be coupled to amino acid uptake at lower pH, but the Na+/K+ ratio of the hemolymph is so low that K+ is probably the major coupling ion in vivo. The neutral amino acid transport system of larval midgut has been studied most extensively. Apart from its cation selectivity, it appears to be related to the amino acid transport system B previously characterized in vertebrate epithelial cells. Both systems have a broad substrate range which excludes 2-(methylamino)-isobutyric acid, an amino acid analog accepted by the mammalian Na(+)-coupled system A. In order to gain insights into the K(+)-coupling mechanism and into amino acid and K+ homeostasis in insects, current studies are designed to delineate the molecular characteristics of these insect transporters. Recent data showed that injection of mRNA prepared from the midgut of Manduca sexta into Xenopus laevis oocytes induced a 1.5- to 2.5-fold stimulation of the Na(+)-dependent uptake of both leucine and phenylalanine (0.2 mmoll-1, pH 8). The molecular cloning of these transporters is now in progress. Knowledge of their unique molecular properties could be exploited in the future to control disease vectors and insect pests.

Molecular cloning and characterization of the vasopressin-regulated urea transporter of rat kidney collecting ducts

Absorption of urea in the renal inner medullary collecting duct (IMCD) contributes to hypertonicity in the medullary interstitium which, in turn, provides the osmotic driving force for water reabsorption. This mechanism is regulated by vasopressin via a cAMP-dependent pathway and activation of a specialized urea transporter located in the apical membrane. We report here the cloning of a novel urea transporter, designated UT1, from the rat inner medulla which is functionally and structurally distinct from the previously reported kidney urea transporter UT2. UT1 expressed in Xenopus oocytes mediated passive transport of urea that was inhibited by phloretin and urea analogs but, in contrast to UT2, was strongly stimulated by cAMP agonists. Sequence comparison revealed that the coding region of UT1 cDNA contains the entire 397 amino acid residue coding region of UT2 and an additional 1,596 basepair-stretch at the 5' end. This stretch encodes a novel 532 amino acid residue NH2-terminal domain that has 67% sequence identity with UT2. Thus, UT1 consists of two internally homologous portions that have most likely arisen by gene duplication. Studies of the rat genomic DNA further indicated that UT1 and UT2 are derived from a single gene by alternative splicing. Based on Northern analysis and in situ hybridization, UT1 is expressed exclusively in the IMCD, particularly in its terminal portion. Taken together, our data show that UT1 corresponds to the previously characterized vasopressin-regulated urea transporter in the apical membrane of the terminal IMCD which plays a critical role in renal water conservation.

Role of lipid peroxidation, trace elements and anti-oxidant enzymes in chronic renal disease patients

Plasma Selenium (Se), Zinc (Zn), Copper (Cu) and Aluminium (Al) levels, red blood cell vitamin E and antioxidant enzymes, glutathione peroxidase (GPX) and catalase activity were studied in 54 patients with renal diseases of different levels of kidney dysfunction. Group I (serum creatinine < 2 mg/dl), Group II (serum creatinine 2-4 mg/dl), Group III (serum creatinine 4.1-8 mg/dl), Group IV (serum creatinine 8.1-12 mg/dl) Group V (serum creatinine > 12 mg/dl); thirty two healthy subjects are controls. Plasma Zn (ug/L) and red blood cell vitamin E (ug/ml PRC) were decreased more significantly than controls (1348.59 +/- 43.72 vs 1318.89 +/- 45.62, and 3.38 +/- 0.45 vs 2.23 +/- 0.52) while plasma Selenium and Copper are within normal ranges. Plasma GSH-PX and catalase activity (IU/ml PRC) were also decreased (28.26 +/- 9.01 vs 20.48 +/- 6.79 and 7.54 +/- 1.91 vs 6.52 +/- 2.31) more significantly than controls. Lipid peroxidation products, plasma (umol/L) and urine malonaldehyde (MDA, umol/Ccr) were elevated (7.29 +/- 3.39 vs 92.94 +/- 61.66, and 32.08 +/- 24.60 vs 246.14 +/- 325.66) significantly (p < 0.0001). The lipid peroxidation abnormalities were seen in patients with normal renal function, which supports the role of oxidative stress early in the course of renal disease. Urine ammonia per GFR was also increased as well as urine B2m and NAG. There was no correlation between lipid peroxidation product (MDA) and any of the antioxidant enzymes, vitamin E, urine NH3, B2m, protein or NAG except urine ammonia and MDA per nephron which correlate with severity of kidney dysfunction which confirmed the role of complex processes in the progression of chronic renal failure. The early intervention to decrease oxygen consumption either by dietary protein restriction antioxidants such as vitamin E supplement or calcium channels blockers may be of value in preserving renal function in the setting of chronic renal failure.

Mammalian urea transporters

Urea transporters are membrane proteins that mediate rapid, passive movement of urea across cell membranes. Physiological studies have revealed their significant roles in urea accumulation in the kidney inner medulla, and consequently in the urinary concentrating mechanism. Three mammalian urea transporters have been identified and their expression in the kidney was found to occur in a tissue-specific manner. This review discusses our current knowledge with emphasis on the localization and regulation of expression of urea transporters in different physiological conditions.

Structure, regulation and physiological roles of urea transporters

Urea is the major constituent of the urine and the principal means for disposal of nitrogen derived from amino acid metabolism. Specialized phloretin-inhibitable urea transporters are expressed in kidney medulla and play a central role in urea excretion and water balance. These transporters allow accumulation of urea in the medulla and enable the kidney to concentrate urine to an osmolality greater than systemic plasma. Recently, expression cloning with Xenopus oocytes has led to the isolation of a novel phloretin-inhibitable urea transporter (UT2) from rabbit, and subsequently from rat kidney. UT2 from both species has the characteristics of the phloretin-sensitive urea transporter previously defined in kidney by in vitro perfused tubule studies. Based on these advances, Ripoche and colleagues cloned a homologous urea transporter (HUT11) from erythrocytes. UT2 and HUT11 predict 43 kDa polypeptides and exhibit 64% amino acid sequence identity. Since regulation of urea transport in the kidney plays an important role in the orchestration of the antidiuretic response, we have studied the regulation of urea transporter in rat kidney at the mRNA level. On Northern blots probed at high stringency, rat UT2 hybridized to two transcripts of 2.9 kb and 4.0 kb, which have spatially distinct distributions within the kidney. Northern analysis and in situ hybridization of kidneys from rats maintained at different physiologic states revealed that the 2.9 and 4.0 kb transcripts are regulated by separate mechanisms. The 4 kb transcript was primarily responsive to changes in the dietary protein content, whereas the 2.9 kb transcript was highly responsive to changes in the hydration state of the animal. We propose that the two UT2 transcripts are regulated by distinct mechanisms to allow optimal fluid balance and urea excretion.

Prevalence of endemic distal renal tubular acidosis and renal stone in the northeast of Thailand

We have previously reported a large group of patients with endemic distal renal tubular acidosis (EdRTA) admitted to the hospitals in the northeast of Thailand. Since large number of patients were identified in a relatively short period of time, and in an area whose population is homogeneous, we were led to investigate the prevalence of the condition in the area. A survey was conducted in five villages (total population of 3,606) within the northeast of Thailand. 3,013 villagers were examined for urinary citrate concentration and short acid loading test was performed in those with low urinary citrate. 2.8% of the population (2.2-3.4%, 95% confidence interval) failed to lower their urine pH after acid loading; within this group, 0.8% of the population had serum potassium less than or equal to 3.5 mEq/l. In addition a large number of villagers were found to have low urinary citrate concentration and there was concurrent high prevalence of renal stone. The prevalence of EdRTA and renal stone was higher in villagers with poorer socioeconomic status, suggesting that environmental factors play a major role in their pathogenesis. Villagers with acidification defect have 2.4 times the chance of having renal stone and/or nephrocalcinosis. EdRTA is therefore one of the important factors responsible for the high prevalence of renal stone in the area. In conclusion we have confirmed the high prevalence of EdRTA in the northeast of Thailand and provided data showing high prevalence of renal stone and hypocitraturia in the same population.

The spectrum of endemic renal tubular acidosis in the northeast of Thailand

We have previously reported a high prevalence of endemic renal tubular acidosis (EnRTA) in the northeast of Thailand, and our subsequent studies provided evidence that K deficiency exists in the same region. Since tubulointerstitial damage is associated with K deficiency, we postulate that this might be implicated in the pathogenesis of EnRTA and, if so, that a spectrum of tubulointerstitial abnormalities can be anticipated. In this study we evaluated renal acidification ability in 4 patients and in 11 of their relatives. We used a 3-day acid load (NH4Cl 0.1 g/kg/day) followed by 20 mg oral furosemide and monitored the maximal renal concentrating ability using water deprivation and intranasal 1-deamino-D-arginine vasopressin. The results showed that the subjects could be divided into three groups; normal relatives of the patients, those with suspected renal tubular acidosis, and patients with overt EnRTA who had chronic metabolic acidosis and a low rate of excretion of NH4+. The rate of excretion of K was very low (20 +/- 4 mmol/day) in patients with EnRTA and in their relatives with suspected EnRTA. The transtubular K concentration gradient was also very low in their relatives, especially in patients with suspected EnRTA (2.8 +/- 0.2). With a 3-day NH4Cl load, the rate of excretion of NH4+ was very low in patients with EnRTA (32 +/- 9 mmol/day), and the relatives with suspected EnRTA also had a decreased capacity to excrete NH+4 (50 +/- 14 mmol/day). In contrast, the normal relatives excreted 92 +/- 12 mmol of NH+4/day. The patients with EnRTA could lower their urine pH to less than 5.5 after the acid loading (6.2 +/- 0.3). After furosemide (20 mg), the NH4+ excretion in the patients with EnRTA was lower than in the normal relatives. Moreover, the minimum urine pH in patients with EnRTA did not fall (6.1 +/- 0.2), but there was a fall to 4.8 +/- 0.1 in the patients with suspected EnRTA after furosemide treatment. In conclusion, there was a spectrum of tubulointerstitial abnormalities ranging from suspected to overt distal RTA in a geographic area known to have a high prevalence of K deficiency. K deficiency might be the important pathogenetic factor of EnRTA in the northeast of Thailand.

Lupus nephritis in Thailand: clinicopathologic findings and outcome in 569 patients

The prognosis of lupus nephritis patients in Thailand has been reported to be poorer than that in Western countries since 1978. After a great evolution in management, we re-evaluate the long-term outcome in patients who were treated and followed up at Siriraj Hospital in Bangkok from 1984 to 1991. Clinical and pathologic records were collected from 569 patients (515 females and 54 men) who were followed up for a mean period of 38.7 +/- 34.6 months. The mean age was 28 +/- 10 years and the median duration of symptoms prior to admission was 7 months. Hypertension was diagnosed in 32.4% of patients and 41.3% had serum creatinine greater than 1.5 mg/dL. Nephrotic-range proteinuria was found in 43.6% of patients and creatinine clearance less than 50 mL/min was found in 58.0%. Of the 314 patients who underwent renal biopsy, the most common histologic finding was diffuse proliferative glomerulonephritis (61.5%). The overall probability of survival was 76.5% at 60 and 90 months after diagnosis. Initial presence of hypertension, renal insufficiency (creatinine clearance < 25 mL/min), and World Health Organization histology class IV and III in the biopsied patients were the three independent factors significantly associated with lower survival probability. Neither gender nor amount of proteinuria was the predictive factor for poor outcome. During the follow-up period, 89 patients died and two patients entered a chronic dialysis program. The two leading causes of death were infection (50.5%) and uremia (28.6%).(ABSTRACT TRUNCATED AT 250 WORDS)

Lupus nephritis in males: 8-year experience at Siriraj Hospital

During 1984 to 1991, 54 out of 569 lupus nephritis patients at Siriraj Hospital were male (F:M sex ratio = 10:1). Mean age of the males was 29.8 +/- 14.6 years, range 12 to 69. The three most common extrarenal manifestations were anemia, cutaneous, and musculoskeletal involvement (74.5, 51.1, and 43.9%, respectively). The major renal manifestations were edema (75.9%) with heavy proteinuria over 3.5 g/day in 62.2% and nephrotic/nephritic findings in 51.9% of cases. Hypertension was found in 35.2%. Mean serum creatinine was 2.0 +/- 1.4 mg/dl while 60.5% of cases had creatinine clearance below 50 ml/minute. Mean serum albumin was 2.6 +/- 0.8 g/dl, cholesterol 262.8 +/- 129.5 and triglycerides 343.2 +/- 244.6 mg/dl. Interestingly, hypercholesterolemia (> 250 mg/dl) was found only in 44.8% of cases with nephrotic syndrome. Antinuclear antibody was demonstrated in 91.5%, anti-dDNA antibody in 64.4% and LE cells in 40.4% of cases. Renal biopsy was done in 45 patients and 30 cases (66.7%) were classified as diffuse proliferative nephritis (WHO type IV), 15.6% of type II, 6.7% each of type III and V, with the rest of type V plus IV (4.4%). Tubulointerstitial inflammation was found in 77.3% of cases. During the follow-up period (42 +/- 35.8 months), 6 patients died. The cause of death were uremia in 3, infection in 2, and cardiac failure in 1. By life-table analysis, the probabilities of survival for 1 and 5 years were 89.5 and 80.6%, respectively. In comparison between sexes, except for a higher amount of urinary protein excretion (4.5 +/- 3.1 vs 3.5 +/- 3.0 g/day, p < 0.05), there were no statistically significant differences in clinical and pathological parameters, and probability of survival.

Lipoprotein abnormalities in adult nephrotic syndrome

The lipid and lipoprotein profiles including apolipoprotein A1 and B100 are measured in 50 idiopathic nephrotic patients (males 26, females 24) with mean age of 32 + 13.6 yrs, serum creatinine 1.32 +/- 0.43 mg/dl compared with 50 age matched normal controls. The renal histology consist of IgM nephropathy 70 per cent, membranous 12 per cent, and IgA 2 per cent. The serum cholesterol, triglycerides, LDL- cholesterol, VLDL-cholesterol, apolipoprotein B (521.6 +/- 201.6, 291.4 +/- 156.2, 438.8 +/- 207.4, 58.3 +/- 31.2, 265.1 +/- 119.8) are statistically significantly higher than controls (p < 0.001). The HDL-cholesterol (30.2 +/- 16.1) is also significantly lower than controls (p < 0.001) but apolipoprotein A is not different from normal subjects. The most common hyperlipoprotein type is type IIb (66%), less common are type IIa (22%), IV (6%) and III (4%) respectively. There is no correlation between serum lipids, lipoproteins and urinary protein, serum albumin, and histological diagnosis. The ratio of cholesterol: HDL, LDL: HDL and Apo A1: B are all significantly higher than normal control (p < 0.001) and correlate with urinary protein levels. This study shows that the nephrotic patients who have persistent heavy proteinuria have dyslipidemia which is highly atherogenic and probably increases the incidence of coronary heart disease.

Should the urine PCO2 or the rate of excretion of ammonium be the gold standard to diagnose distal renal tubular acidosis?

A high rate of excretion of ammonium (NH4+) during chronic metabolic acidosis should rule out the diagnosis of distal renal tubular acidosis (RTA). Bearing this in mind, the purpose of this report is to demonstrate that a low urine minus blood PCO2 difference in alkaline urine (U-B PCO2) is a less reliable indicator of the diagnosis of distal RTA. The patient who is the subject of this report sniffs glue on a chronic, but intermittent basis. He presented with metabolic acidosis (pH 7.20; bicarbonate, 10 mmol/L) and an anion gap in plasma of 20 mEq/L. The urine anion gap (-14 mEq/L) and osmolal gap (185 mmol/L [mOsm/kg] H2O) suggested that there was a high, rather than a low, rate of excretion of NH4+. This was confirmed by direct measurement of NH4+ in the urine (101 mumol/min). The high rate of excretion of NH4+ suggested that the metabolic acidosis was due, in large part, to an abnormally high rate of production of acid (hippuric acid, because the rate of excretion of hippurate was 76 mumol/min). The U-B PCO2 was low (10 mm Hg) on the second hospital day, after the acidosis was corrected. Potential reasons for the discrepancy between the high rate of excretion of NH4+ and the low U-B PCO2 are discussed.