Hyperfiltration and uricosuria in adolescents with type 1 diabetes

Glomerular hyperfiltration: part 2-clinical significance in children

Glomerular hyperfiltration (GHF) is a phenomenon that can occur in various clinical conditions affecting the kidneys such as sickle cell disease, diabetes mellitus, autosomal dominant polycystic kidney disease, and solitary functioning kidney. Yet, the pathophysiological mechanisms vary from one disease to another and are not well understood. More so, it has been demonstrated that GHF may occur at the single-nephron in some clinical conditions while in others at the whole-kidney level. In this review, we explore the pathophysiological mechanisms of GHF in relation to various clinical conditions in the pediatric population. In addition, we discuss the role and mechanism of action of important factors such as gender, low birth weight, and race in the pathogenesis of GHF. Finally, in this current review, we further highlight the consequences of GHF in the progression of kidney disease.

Association between serum uric acid levels and cardiovascular risk factors among adults in India

BACKGROUND AND AIM

The objective of this study was to explore the association between serum uric acid (SUA) levels and cardiovascular risk factors in the Indian population.

METHODS AND RESULTS

This was a cross-sectional, population-based study. The study enrolled adults aged 20 years and above residing in rural, sub-urban, and urban. All participants completed a detailed questionnaire, underwent anthropometric measurements, and had blood samples collected. Participants were divided into three tertiles based on their SUA concentrations. A total of 2976 participants were included in this study, with 865 from rural, 1030 from sub-urban, and 1081 from urban populations. The mean values of cardiovascular risk factors were significantly higher in tertile 3 (p < 0.001) as compared to the other tertiles. However, we observed a negative trend between the increase of SUA and SUA/Scr ratio and HbA1c levels (Pearson correlation r = -0.068; p < 0.001 and r = -0.140; p < 0.001, respectively). The healthy and prediabetic groups did not show any significant change in HbA1c with increasing SUA levels, while an inverse trend was observed in diabetics. In the diabetic population, both men and women showed an inverse trend between increasing SUA levels and HbA1c in both known and newly diagnosed diabetes (p < 0.001).

CONCLUSIONS

The study found a positive association between SUA levels and cardiovascular risk factors. However, HbA1c was inversely correlated with increasing SUA tertiles in both known and newly diagnosed diabetes, as compared to the general population. Additionally, both men and women with diabetes consistently showed an inverse relationship between increasing SUA/SCr ratio and HbA1c levels.

Purine Metabolism Dysfunctions: Experimental Methods of Detection and Diagnostic Potential

Purines, such as adenine and guanine, perform several important functions in the cell. They are found in nucleic acids; are structural components of some coenzymes, including NADH and coenzyme A; and have a crucial role in the modulation of energy metabolism and signal transduction. Moreover, purines have been shown to play an important role in the physiology of platelets, muscles, and neurotransmission. All cells require a balanced number of purines for growth, proliferation, and survival. Under physiological conditions, enzymes involved in purines metabolism maintain a balanced ratio between their synthesis and degradation in the cell. In humans, the final product of purine catabolism is uric acid, while most other mammals possess the enzyme uricase that converts uric acid to allantoin, which can be easily eliminated with urine. During the last decades, hyperuricemia has been associated with a number of human extra-articular diseases (in particular, the cardiovascular ones) and their clinical severity. In this review, we go through the methods of investigation of purine metabolism dysfunctions, looking at the functionality of xanthine oxidoreductase and the formation of catabolites in urine and saliva. Finally, we discuss how these molecules can be used as markers of oxidative stress.

Longitudinal uric acid has nonlinear association with kidney failure and mortality in chronic kidney disease

We investigated the shape of the relationship between longitudinal uric acid (UA) and the hazard of kidney failure and death in chronic kidney disease (CKD) patients, and attempted to identify thresholds associated with increased hazards. We included CKD stage 3-5 patients from the CKD-REIN cohort with one serum UA measurement at cohort entry. We used cause-specific multivariate Cox models including a spline function of current values of UA (cUA), estimated from a separate linear mixed model. We followed 2781 patients (66% men, median age, 69 years) for a median of 3.2 years with a median of five longitudinal UA measures per patient. The hazard of kidney failure increased with increasing cUA, with a plateau between 6 and 10 mg/dl and a sharp increase above 11 mg/dl. The hazard of death had a U-shape relationship with cUA, with a hazard twice higher for 3 or 11 mg/dl, compared to 5 mg/dl. In CKD patients, our results indicate that UA above 10 mg/dl is a strong risk marker for kidney failure and death and that low UA levels below 5 mg/dl are associated with death before kidney failure.

Urinalysis of individuals with renal hyperfiltration using ATR-FTIR spectroscopy

Abnormal increased glomerular filtration rate (GFR), otherwise known as renal hyperfiltration (RHf), is associated with an increased risk of chronic kidney disease and cardiovascular mortality. Although it is not considered as a disease alone in medicine today, early detection of RHf is essential to reducing risk in a timely manner. However, detecting RHf is a challenge since it does not have a practical biochemical marker that can be followed or quantified. In this study, we tested the ability of ATR-FTIR spectroscopy to distinguish 17 individuals with RHf (hyperfiltraters; RHf (+)), from 20 who have normal GFR (normofiltraters; RHf(-)), using urine samples. Spectra collected from hyperfiltraters were significantly different from the control group at positions 1621, 1390, 1346, 933 and 783/cm. Intensity changes at these positions could be followed directly from the absorbance spectra without the need for pre-processing. They were tentatively attributed to urea, citrate, creatinine, phosphate groups, and uric acid, respectively. Using principal component analysis (PCA), major peaks of the second derivative forms for the classification of two groups were determined. Peaks at 1540, 1492, 1390, 1200, 1000 and 840/cm were significantly different between the two groups. Statistical analysis showed that the spectra of normofiltraters are similar; however, those of hyperfiltraters show diversity at multiple positions that can be observed both from the absorbance spectra and the second derivative profiles. This observation implies that RHf can simultaneously affect the excretion of many substances, and that a spectroscopic analysis of urine can be used as a rapid and non-invasive pre-screening tool.

Research progress of risk factors and early diagnostic biomarkers of gout-induced renal injury

Gout renal injury has an insidious onset, no obvious symptoms, and laboratory abnormalities in the early stages of the disease. The injury is not easily detected, and in many cases, the patients have entered the renal failure stage at the time of diagnosis. Therefore, the detection of gout renal injury–related risk factors and early diagnostic biomarkers of gout renal injury is essential for the prevention and early diagnosis of the disease. This article reviews the research progress in risk factors and early diagnostic biomarkers of gout renal injury.

Tubular injury in diabetic ketoacidosis: Results from the diabetic kidney alarm study

OBJECTIVE

Glomerular injury is a recognized complication of diabetic ketoacidosis (DKA), yet the tubular lesions are poorly understood. The aim of this prospective study was to evaluate the presence and reversibility of tubular injury during DKA in children with type 1 diabetes (T1D).

RESEARCH DESIGN AND METHODS

Blood and urine samples were collected from 40 children with DKA (52% boys, mean age 11 ± 4 years, venous pH 7.2 ± 0.1, glucose 451 ± 163 mg/dL) at three timepoints: 0-8 and 12-24 h after starting insulin, and 3 months after discharge. Mixed-effects models evaluated the changes in tubular injury markers over time (neutrophil gelatinase-associated lipocalin [NGAL], kidney injury molecule 1 [KIM-1], and interleukin 18 [IL-18]). We also evaluated the relationships among the tubular injury biomarkers, copeptin, a vasopressin surrogate, and serum uric acid (SUA).

RESULTS

Serum NGAL, KIM-1, and IL-18 were highest at 0-8 h (306.5 ± 45.9 ng/mL, 128.9 ± 10.1 pg/mL, and 564.3 ± 39.2 pg/mL, respectively) and significantly decreased over 3 months (p = 0.03, p = 0.01, and p < 0.001, respectively). There were strong relationships among increases in copeptin and SUA and rises in tubular injury biomarkers. At 0-8 h, participants with acute kidney injury (AKI) [17%] showed significantly higher concentrations of tubular injury markers, copeptin, and SUA.

CONCLUSIONS

DKA was characterized by tubular injury, and the degree of injury associated with elevated copeptin and SUA. Tubular injury biomarkers, copeptin and SUA may be able to predict AKI in DKA.

Hyperuricemia and Progression of Chronic Kidney Disease: A Review from Physiology and Pathogenesis to the Role of Urate-Lowering Therapy

The relationship between hyperuricemia, gout, and renal disease has been investigated for several years. From the beginning, kidney disease has been considered a complication of gout; however, the viewpoints changed, claiming that hypertension and elevated uric acid (UA) levels are caused by decreased urate excretion in patients with renal impairment. To date, several examples of evidence support the role of hyperuricemia in cardiovascular or renal diseases. Several mechanisms have been identified that explain the relationship between hyperuricemia and chronic kidney disease, including the crystal effect, renin-angiotensin-aldosterone system activation, nitric oxide synthesis inhibition, and intracellular oxidative stress stimulation, and urate-lowering therapy (ULT) has been proven to reduce renal disease progression in the past few years. In this comprehensive review, the source and physiology of UA are introduced, and the mechanisms that explain the reciprocal relationship between hyperuricemia and kidney disease are reviewed. Lastly, current evidence supporting the use of ULT to postpone renal disease progression in patients with hyperuricemia and gout are summarized.

Acute Kidney Injury in Pediatric Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common complication of type 1 and 2 diabetes and often presents during adolescence and young adulthood. Given the growing incidence of both type 1 and type 2 diabetes in children and adolescents, DKD represents a significant public health problem. Acute kidney injury (AKI) in youth with diabetes is strongly associated with risk of DKD development. This review will summarize the epidemiology and pathophysiology of AKI in children with diabetes, the relationship between AKI and DKD, and the potential therapeutic interventions. Finally, we will appraise the impact of the recent COVID-19 infection pandemic on AKI in children with diabetes.

Different alterations of glomerular filtration rate and their association with uric acid in children and adolescents with type 1 diabetes or with overweight/obesity

BACKGROUND

Hyperfiltration (HF) occurs early in diabetes or obesity (OB)-associated renal disease. Alterations of glomerular filtration rate (GFR) in childhood OB remain unclear.

OBJECTIVES

To compare the prevalence of GFR alterations and its association with uric acid in children and adolescents with type 1 diabetes (T1D) vs overweight (OW)/OB.

METHODS

Cross-sectional study of 29 youths (aged: 13 ± 2 years) with T1D (disease duration: 7 ± 3 years) and 165 with OW/OB (aged: 11 ± 3 years). Patients with an albumin-creatinine ratio >3.39 mg/mmol were excluded. GFR was estimated with creatinine-cystatin C Zappitelli equation. HF and low GFR were defined by a GFR > 135 and <90 mL/min.1.73 m² , respectively.

RESULTS

HF was higher in children with T1D vs OW/OB (28% vs 10%, P < .005). Children with OW/OB also showed a 10% of low GFR. In patients with T1D, HbA1c (β = .8, P < .001), and systolic blood pressure (β = 11.4, P < .005) were independent predictors of GFR (R² = .65). In OW/OB, HF cases were almost limited to prepubertal children and low GFR to pubertal ones. GFR in OW/OB was associated with age (β = -2.2, P < .001), male sex (β = -11.6, P < .001), and uric acid (β = -.05, P < .001) in adjusted models (R² = .33).

CONCLUSIONS

GFR alterations were different between youths with T1D and with OW/OB. Higher uric acid, older age, and puberty were related to lower GFR values in OW/OB children. Longitudinal studies will determine if low GFR is consequence of a rapid GFR decline in pediatric patients with OW/OB.

The case for uric acid-lowering treatment in patients with hyperuricaemia and CKD

Hyperuricaemia is common among patients with chronic kidney disease (CKD), and increases in severity with the deterioration of kidney function. Although existing guidelines for CKD management do not recommend testing for or treatment of hyperuricaemia in the absence of a diagnosis of gout or urate nephrolithiasis, an emerging body of evidence supports a direct causal relationship between serum urate levels and the development of CKD. Here, we review randomized clinical trials that have evaluated the effect of urate-lowering therapy (ULT) on the rate of CKD progression. Among trials in which individuals in the control arm experienced progressive deterioration of kidney function (which we define as ≥4 ml/min/1.73 m² over the course of the study - typically 6 months to 2 years), treatment with ULT conferred consistent clinical benefits. In contrast, among trials where clinical progression was not observed in the control arm, treatment with ULT was ineffective, but this finding should not be used as an argument against the use of uric acid-lowering therapy. Although additional studies are needed to identify threshold values of serum urate for treatment initiation and to confirm optimal target levels, we believe that sufficient evidence exists to recommend routine measurement of serum urate levels in patients with CKD and consider initiation of ULT among those who are hyperuricaemic with evidence of deteriorating renal function, unless specific contraindications exist.

Hyperuricemia, urine uric excretion, and associated complications in thalassemia patients

Thalassemia patients have a high cell turnover rate due to chronic hemolysis and ineffective erythropoiesis; therefore, hyperuricemia is anticipated. This study aimed to identify the prevalence of hyperuricemia, gout and nephrolithiasis, conditions associated with serum uric acid (SUA), and urine uric acid excretion (UUA) in thalassemia patients. This was a cross-sectional study in patients aged 15 years or older at Chiang Mai University Hospital. All patients had blood and 24-h urine collection test. We enrolled 112 thalassemia patients in which 67.0% were female, 64.3% had beta thalassemia/Hb E, 76.8% were transfusion dependent, and 59.8% were post splenectomy. The median age was 29 (16-58) years. Mean SUA was 6.7 ± 2.0 mg/dl and hyperuricemia (SUA > 6.8 mg/dl) was found in 47 cases (45.2%). Intact spleen (ORs 4.3, 95%CI 1.55-12.50, p = 0.01) and lower FEuric (ORs 2.08, 95%CI 1.35-3.33, p < 0.01) were associated with hyperuricemia significantly. Seven (6.3%) had gouty arthritis and nine (8%) had microscopic hematuria, one case being confirmed nephrolithiasis. The mean UUA excretion was 981.3 ± 335.0 mg/day and UUA hyperexcretion (> 700 mg/24 h) was found in 83.3%. UUA hyperexcretion patients had renal hyperfiltration 46%, glomerular dysfunction 84%, and tubular dysfunction 7.7%. From our study, hyperuricemia was found in approximately 40% of thalassemia patients but gouty arthritis occurred only in few patients (6%). This may be explained by urinary uric hyperexcretion which is found in over 80%. The significant risk factors for hyperuricemia were intact spleen and lower fraction excretion of uric acid.

Pink Urine Syndrome: A Combination of Insulin Resistance and Propofol

Pink urine syndrome is mostly seen in patients treated with propofol anesthesia. The pink color is attributed to the presence of large concentrations of uric acid (and pigment), which is excreted in large amounts when propofol is given. We describe a case of propofol-induced pink urine syndrome and perform a comprehensive, evidence-based review. We discuss prior case studies already published in the literature as we speculate on the pathophysiology and how it translates to a clinically relevant entity.

Sex-related association of serum uric acid with inflammation, kidney function and blood pressure in type 1 diabetic patients

BACKGROUND/OBJECTIVE

Recent studies suggest that uric acid (UA) is a mediator of diabetic nephropathy. We hypothesized that serum UA would associate with the prevalence of diabetic nephropathy in youth with type 1 diabetes (T1D), and that this relationship would differ by sex.

METHODS

We examined 120 young boys and the same number of girls with T1D. C-reactive protein (CRP), interleukin-6 (IL-6), interleukin-10 (IL-10), tumor necrosis factor α (TNF-α), UA, cystatin C serum concentrations, albumin excretion rate and blood pressure were also analyzed.

RESULTS

T1D boys had higher serum UA and creatinine concentration, as well as albumin excretion rate and estimated glomerular filtration rate than T1D girls. Moreover, newly diagnosed nephropathy was more common in male subjects in comparison to female patients. Only in T1D boys serum UA was positively correlated with concentrations of subclinical inflammatory markers (CRP, IL-6, TNF-α), the indicators of renal function (albumin excretion rate, serum cystatin C level), blood pressure and negatively correlated with anti-inflammatory IL-10. In addition, only in T1D girls serum UA concentration was negatively correlated with hemoglobin A1c.

CONCLUSIONS

Serum UA is associated with nephropathy prevalence, albeit only in boys with T1D and may be an important risk factor for predicting diabetes-related cardiorenal complications in these patients.

Role of bicarbonate supplementation on urine uric acid crystals and diabetic tubulopathy in adults with type 1 diabetes

Uricosuria and crystallization are increasingly recognized risk factors for diabetic tubulopathy. This pilot clinical trial aimed to determine the acute effect of urinary alkalinization using oral sodium bicarbonate (NaHCO₃ ) on UA crystals in adults with type 1 diabetes (T1D). Adults with T1D, ages 18 to 65 years (n = 45, 60% female, HbA1c, 7.5 ± 1.2%, 20.2 ± 9.3 years duration) without chronic kidney disease (eGFR ≥60 mL/min/1.73 m² and albumin-to-creatinine ratio < 30 mg/g) received 2 doses of 1950 mg oral NaHCO₃ over 24 hours. Fasting urine and serum were collected pre- and post-intervention. UA crystals were identified under polarized microscopy. Urine measurements included: osmolality, pH, UA, creatinine and kidney injury molecule-1 (KIM-1). NaHCO₃ therapy increased mean ± SD urine pH from 6.1 ± 0.7 to 6.5 ± 0.7 (P < .0001). Prior to therapy, 31.0% of participants had UA crystals vs 6.7% post therapy (P = .005). Change in urine pH inversely correlated with change in urine KIM-1 (r:-0.51, P = .0003). In addition, change in urine UA over 24 hours correlated with change in urine KIM-1 (r:0.37, P = .01). In conclusion, oral NaHCO₃ normalized urine pH and decreased UA crystals, and may hold promise as an inexpensive and safe tubulo-protective intervention in individuals with T1D.

Hyperfiltration, urinary albumin excretion, and ambulatory blood pressure in adolescents with Type 1 diabetes mellitus

Adolescents with Type 1 diabetes mellitus (T1DM) are at risk for hyperfiltration and elevated urinary albumin-to-creatinine ratio (ACR), which are early indicators of diabetic nephropathy. Adolescents with T1DM also develop early changes in blood pressure, cardiovascular structure, and function. Our aims were to define the relationships between hyperfiltration, ACR, and 24-h ambulatory blood pressure over time in adolescents with T1DM. Normotensive, normoalbuminuric adolescents ( n = 98) with T1DM underwent baseline and 2-yr 24-h ambulatory blood pressure monitoring, glomerular filtration rate (eGFR) estimated by cystatin C (Larsson equation), and ACR measurements. Linear regression models adjusted for diabetes duration, sex, and HbA1c were used to determine associations. Hyperfiltration (eGFR ≥ 133 ml/min) was present in 31% at baseline and 21% at 2-yr follow-up. Hyperfiltration was associated with greater odds of rapid GFR decline (>3 ml·min-1·yr-1) [OR: 5.33, 95%; CI: 1.87-15.17; P = 0.002] over 2 yr. Natural log of ACR at baseline was associated with greater odds of hyperfiltration (OR: 1.71, 95% CI: 1.00-2.92; P = 0.049) and 2-yr follow-up (OR: 2.14, 95%; CI: 1.09-4.19; P = 0.03). One SD increase in eGFR, but not ln ACR, at 2-yr follow-up conferred greater odds of nighttime nondipping pattern (OR: 1.96, 95% CI: 1.06-3.63; P = 0.03). Hyperfiltration was prevalent at baseline and at 2-yr follow-up, predicted rapid decline in GFR, and was related to ACR. Elevated GFR at 2-yr follow-up was associated with nighttime nondipping pattern. More work is needed to better understand early relationships between renal hemodynamic and systemic hemodynamic changes in adolescents with T1DM to reduce future cardiorenal complications.

Uric acid in the pathogenesis of metabolic, renal, and cardiovascular diseases: A review

The association between uric acid (UA) on one side and systemic hypertension (Htn), dyslipidemia, glucose intolerance, overweight, fatty liver, renal disease and cardiovascular disease (CVD) on the other side is well recognized. However, the causal relationship between UA and these different clinical problems is still debatable. The recent years have witnessed hundreds of experimental and clinical trials that favored the opinion that UA is a probable player in the pathogenesis of these disease entities. These studies disclosed the strong association between hyperuricemia and metabolic syndrome (MS), obesity, Htn, type 2 diabetes mellitus (DM), non-alcoholic fatty liver disease, hypertriglyceridemia, acute kidney injury, chronic kidney disease (CKD), coronary heart disease (CHD), heart failure and increased mortality among cardiac and CKD patients. The association between UA and nephrolithiasis or preeclampsia is a non-debatable association. Recent experimental trials have disclosed different changes in enzyme activities induced by UA. Nitric oxide (NO) synthase, adenosine monophosphate kinase (AMPK), adenosine monophosphate dehydrogenase (AMPD), and nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase are affected by UA. These changes in enzymatic activities can lead to the observed biochemical and pathological changes associated with UA. The recent experimental, clinical, interventional, and epidemiologic trials favor the concept of a causative role of UA in the pathogenesis of MS, renal, and CVDs.

Renal and Vascular Effects of Uric Acid Lowering in Normouricemic Patients With Uncomplicated Type 1 Diabetes

Higher plasma uric acid (PUA) levels are associated with lower glomerular filtration rate (GFR) and higher blood pressure (BP) in patients with type 1 diabetes (T1D). Our aim was to determine the impact of PUA lowering on renal and vascular function in patients with uncomplicated T1D. T1D patients (n = 49) were studied under euglycemic and hyperglycemic conditions at baseline and after PUA lowering with febuxostat (FBX) for 8 weeks. Healthy control subjects were studied under normoglycemic conditions (n = 24). PUA, GFR (inulin), effective renal plasma flow (para-aminohippurate), BP, and hemodynamic responses to an infusion of angiotensin II (assessment of intrarenal renin-angiotensin-aldosterone system [RAAS]) were measured before and after FBX treatment. Arterial stiffness, flow-mediated dilation (FMD), nitroglycerin-mediated dilation (GMD), urinary nitric oxide (NO), and inflammatory markers were measured before and after FBX treatment. Gomez equations were used to estimate arteriolar afferent resistance, efferent resistance (R_E), and glomerular hydrostatic pressure (P_GLO). FBX had a modest systolic BP-lowering effect in T1D patients (112 ± 10 to 109 ± 9 mmHg, P = 0.049) without impacting arterial stiffness, FMD, GMD, or NO. FBX enhanced the filtration fraction response to hyperglycemia in T1D patients through larger increases in R_E, P_GLO, and interleukin-18 but without impacting the RAAS. FBX lowered systolic BP and modulated the renal R_E responses to hyperglycemia but without impacting the RAAS or NO levels, suggesting that PUA may augment other hemodynamic or inflammatory mechanisms that control the renal response to hyperglycemia at the efferent arteriole. Ongoing outcome trials will determine cardiorenal outcomes of PUA lowering in patients with T1D.

The Gomez' equations and renal hemodynamic function in kidney disease research

Diabetic kidney disease (DKD) remains the leading cause of end-stage renal disease. A major challenge in preventing DKD is the difficulty in identifying high-risk patients at an early, pre-clinical stage. Albuminuria and eGFR as measures of renal function in DKD research and clinical practice are limited by regression of one-third of patients with microalbuminuria to normoalbuminuria and eGFR is biased and imprecise in the normal-elevated range. Moreover, existing methods that are used to assess renal function do not give detailed insight into the location of the renal hemodynamic effects of pharmacological agents at the segmental level. To gain additional information about the intrarenal circulation in-vivo in humans, mathematical equations were developed by Gomez et al in the 1950s. These equations used measurements of GFR, renal blood flow (RBF), effective renal plasma flow (ERPF), renal vascular resistance (RVR), hematocrit and serum protein to calculate afferent and efferent arteriolar resistances, glomerular hydrostatic pressure and filtration pressure. Although indirect and based on physiological assumptions, these techniques have the potential to improve researchers' ability to identify early pre-clinical changes in renal hemodynamic function in patients with a variety of conditions including DKD, thereby offering tremendous potential in mechanistic human research studies. In this review, we focus on the application of Gomez' equations and summarize the potential and limitations of this technique in DKD research. We also summarize illustrative data derived from Gomez' equations in patients with type 1 (T1D) and type 2 diabetes (T2D) and hypertension.