The effect of n-3 long-chain polyunsaturated fatty acid supplementation on urine protein excretion and kidney function: meta-analysis of clinical trials

Association between fish consumption and nephropathy in American Indians--the Strong Heart Study

OBJECTIVE

The present study examined the association between fish consumption and nephropathy in American Indians.

METHODS

In the family cohort of the Strong Heart Study, we investigated 2,261 participants with baseline examination between 2001 and 2003 and follow-up examination between 2006 and 2008. The average follow-up period was 5.4 years. We defined fish consumption as the sum of dietary intake of tuna, fried fish, and nonfried fish obtained from a validated food frequency questionnaire. Nephropathy was defined as microalbuminuria (urinary albumin-creatinine ratio [ACR]: 30 to 299 mg/g), macroalbuminuria (urinary ACR: ≥ 300 mg/g), or an estimated glomerular filtration rate of <60 mL/min/1.73 m(2). Using regression models, we examined the association between fish consumption measured at baseline and 2 outcomes in nephropathy present at follow-up, albuminuria, or renal impairment, and change in urinary ACR or estimated glomerular filtration rate between baseline and follow-up examinations.

RESULTS

The prevalence of microalbuminuria, macroalbuminuria, and renal impairment was 13%, 3%, and 4%, respectively. The fish items consumed by the participants were predominantly deep-fried. We found no associations between fish consumption and any measure of nephropathy after adjusting for demographic, clinical, lifestyle, and dietary factors.

CONCLUSIONS

Dietary intake of predominantly fried fish was not associated with a lower risk of nephropathy in American Indians.

Off the beaten renin-angiotensin-aldosterone system pathway: new perspectives on antiproteinuric therapy

CKD is a major public health problem in the developed and the developing world. The degree of proteinuria associated with renal failure is a generally well accepted marker of disease severity. Agents with direct antiproteinuric effects are highly desirable therapeutic strategies for slowing, or even halting, progressive loss of kidney function. We review progress on therapies acting further downstream of the renin-angiotensin-aldosterone system pathway (e.g., transforming growth factor-beta antagonism, endothelin antagonism) and on those acting independent of the renin-angiotensin-aldosterone system pathway. In all, we discuss 26 therapeutic targets or compounds and 2 lifestyle changes (dietary modification and weight loss) that have been used clinically for diabetic or nondiabetic kidney disease. These therapies include endogenous molecules (estrogens, isotretinoin), biologic antagonists (monoclonal antibodies, soluble receptors), and small molecules. Where mechanistic data are available, these therapies have been shown to exert favorable effects on glomerular cell phenotype. In some cases, recent work has indicated surprising new molecular pathways for some therapies, such as direct effects on the podocyte by glucocorticoids, rituximab, and erythropoietin. It is hoped that recent advances in the basic science of kidney injury will prompt development of more effective pharmaceutical and biologic therapies for proteinuria.

Dietary intake of eicosapentaenoic and docosahexaenoic acid and diabetic nephropathy: cohort analysis of the diabetes control and complications trial

OBJECTIVE

To investigate the association between dietary n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) and the degree and development of albuminuria in type 1 diabetes.

RESEARCH DESIGN AND METHODS

We analyzed longitudinal data from 1,436 participants in the Diabetes Control and Complications Trial. We defined the average intake of eicosapentaenoic and docosahexaenoic acid from diet histories. Urinary albumin excretion rates (UAERs) were measured over 24 h; incident albuminuria was considered the first occurrence of an UAER >40 mg/24 h sustained for >or=1 year in normoalbuminuric individuals. RESULTS In a mean follow-up of 6.5 years, we observed a lower mean UAER (difference 22.7 mg/24 h [95% CI 1.6-43.8)]) in the top versus the bottom third of dietary n-3 LC-PUFAs, but we found no association with incident albuminuria.

CONCLUSIONS

Dietary n-3 LC-PUFAs appear inversely associated with the degree but not with the incidence of albuminuria in type 1 diabetes. These findings require further investigation in prospective studies.

Omega-3 polyunsaturated fatty acids in the treatment of kidney disease

After more than 25 years of published investigation, including randomized controlled trials, the role of omega-3 polyunsaturated fatty acids in the treatment of kidney disease remains unclear. In vitro and in vivo experimental studies support the efficacy of omega-3 polyunsaturated fatty acids on inflammatory pathways involved with the progression of kidney disease. Clinical investigations have focused predominantly on immunoglobulin A (IgA) nephropathy. More recently, lupus nephritis, polycystic kidney disease, and other glomerular diseases have been investigated. Clinical trials have shown conflicting results for the efficacy of omega-3 polyunsaturated fatty acids in IgA nephropathy, which may relate to varying doses, proportions of eicosapentaenoic acid and docosahexaenoic acid, duration of therapy, and sample size of the study populations. Meta-analyses of clinical trials using omega-3 polyunsaturated fatty acids in IgA nephropathy have been limited by the quality of available studies. However, guidelines suggest that omega-3 polyunsaturated fatty acids should be considered in progressive IgA nephropathy. Omega-3 polyunsaturated fatty acids decrease blood pressure, a known accelerant of kidney disease progression. Well-designed, adequately powered, randomized, controlled clinical trials are required to further investigate the potential benefits of omega-3 polyunsaturated fatty acids on the progression of kidney disease and patient survival.

Manifestation of renal disease in obesity: pathophysiology of obesity-related dysfunction of the kidney

Albuminuria in individuals whose body mass index exceeds 40 kg/m(2) is associated with the presence of large glomeruli, thickened basement membrane and epithelial cellular (podocyte) distortion. Obstructive sleep apnea magnifies glomerular injury as well, probably through a vasoconstrictive mechanism. Insulin resistance from excess fatty acids is exacerbated by decreased secretion of high molecular weight adiponectin from adipose cells in the obese state. Adiponectin potentiates insulin in its post-receptor signaling resulting in glucose oxidation in mitochondria. Recent studies of podocyte physiology have concentrated on the structural and functional requirements that prevent glomerular albumin leakage. The architecture of the podocyte involves nephrin and podocin, proteins that cooperate to keep slit pores between foot processes competent to retain albumin. Insulin and adiponectin are necessary for high-energy phosphate generation. When fatty acids bind to albumin, the toxicity to proximal renal tubules is magnified. Albumin and fatty acids are elevated in urine of individuals with obesity related nephrotic syndrome. Fatty acid accumulation and resistin inhibit insulin and adiponectin. Study of cytokines produced by adipose tissue (adiponectin and leptin) and macrophages (resistin) has led to a better understanding of the relationship between weight and hypertension. Leptin, is presumably secreted after food intake to inhibit the midbrain/hypothalamic appetite centers. Resistance to leptin results in excess signaling to hypothalamic sympathetics leading to hypertension. Demonstration of the existence of a cerebral receptor mutation provide evidence for a role in hypertension of a central nervous reflex arc in humans. Further understanding of obesity-related renal dysfunction has been accomplished recently using experimental models. Rapid weight loss following bariatric surgery may reverse renal pathology of obesity with restoration of normal blood pressure.