Fatty acids and idiopathic calcium nephrolithiasis

Adherence to the Mediterranean Dietary Pattern and Incidence of Nephrolithiasis in the Seguimiento Universidad de Navarra Follow-up (SUN) Cohort

BACKGROUND

Diet plays an important role in the pathogenesis of nephrolithiasis. Limited data are available to investigate the association between a Mediterranean dietary pattern and risk for nephrolithiasis.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

16,094 men and women without a history of nephrolithiasis who participated in the Seguimiento Universidad de Navarra Follow-up (SUN) Project.

PREDICTORS

A validated 136-item food frequency questionnaire was used to assess baseline adherence to a Mediterranean dietary pattern that is high in fruits, vegetables, nuts, fish, and legumes, but moderate in alcohol and low in meats, saturated fats, and sugars. A Mediterranean dietary pattern score was calculated and categorized into 3 groups (0-3, 4-6, and 7-9 points). Additional factors included in statistical models were sex, age, body mass index, smoking, physical activity, time spent watching television, following a medical nutritional therapy, water and energy intake, calcium and vitamin D supplementation, and history of hypertension or diabetes.

OUTCOMES

Incidence of nephrolithiasis. Participants were classified as having incident nephrolithiasis if they reported a physician-made diagnosis of nephrolithiasis during follow-up.

RESULTS

After a mean follow-up of 9.6 years, 735 new cases of nephrolithiasis were identified. The multivariable HRs of nephrolithiasis for the 2 highest categories of adherence to the Mediterranean dietary pattern, using the lowest category as the reference, were 0.93 (95% CI, 0.79-1.09) and 0.64 (95% CI, 0.48-0.87); P for trend=0.01. The risk for nephrolithiasis was lower with greater consumption of dairy products and vegetables and greater with higher monounsaturated fatty acid to saturated fatty acid ratio.

LIMITATIONS

No information for kidney stone composition.

CONCLUSIONS

Greater adherence to a Mediterranean dietary pattern was associated with reduced risk for incident nephrolithiasis. Additional longitudinal studies are needed.

Review of the pathophysiological aspects involved in urological disease associated with metabolic syndrome

INTRODUCTION

Metabolic syndrome is a constellation of disorders that includes insulin resistance, central obesity, arterial hypertension and hyperlipidaemia. These disorders can have implications for the genitourinary apparatus.

OBJECTIVES

To conduct a review on the pathophysiological aspects that explain the relationship between metabolic syndrome and sexual dysfunction, lower urinary tract syndrome, prostate cancer and stone disease.

METHODS

We performed a qualitative, narrative literature review through a literature search on PubMed of articles published between 1997 and 2015, using the terms pathophysiology, metabolic syndrome, endothelial dysfunction, lipotoxicity, mitochondrial dysfunction, kidney stones, hypogonadism, erectile dysfunction, lower urinary tract syndrome and prostate cancer.

SYNTHESIS OF THE EVIDENCE

Metabolic syndrome constitutes an established complex of symptoms, defined as the presence of insulin resistance, central obesity, hypertension and hyperlipidaemia. Endothelial dysfunction secondary to lipotoxicity generates an inflammatory state, which involves renal cell metabolism, vascularisation of the pelvis and androgen production. These facts explain the relationship between metabolic syndrome, nephrolithiasis, lower urinary tract syndrome, hypogonadism and erectile dysfunction in men.

CONCLUSIONS

Strategies such as proper diet, regular exercise, insulin treatment, testosterone-replacement therapy, therapy with antioxidants and free-radical inhibitors and urological treatments classically used for lower urinary tract syndrome have shown promising results in this syndrome.

Mechanism of modulation of the plasma membrane Ca(2+)-ATPase by arachidonic acid

The intracellular level of long chain fatty acids controls the Ca(2+) concentration in the cytoplasm. The molecular mechanisms underlying this Ca(2+) mobilization are not fully understood. We show here that the addition of low micromolar concentrations of fatty acids directly to the purified plasma membrane Ca(2+)-ATPase enhance ATP hydrolysis, while higher concentration decrease activity, exerting a dual effect on the enzyme. The effect of arachidonic acid is similar in the presence or absence of calmodulin, acidic phospholipids or ATP at the regulatory site, thereby precluding these sites as probable acid binding sites. At low arachidonic acid concentrations, neither the affinity for calcium nor the phosphoenzyme levels are significantly modified, while at higher concentrations both are decreased. The action of arachidonic acid is isoenzyme specific. The increase on ATP hydrolysis, however, is uncoupled from calcium transport, because arachidonic acid increases the permeability of erythrocyte membranes to calcium. Oleic acid has no effect on membrane permeability while linoleic acid shows an effect similar to that of arachidonic acid. Such effects might contribute to the entry of extracellular Ca(2+) following to fatty acid release.

Bone disease and idiopathic hypercalciuria

Observational and epidemiologic studies alike have shown that idiopathic hypercalciuric (IH) stone-forming patients typically show bone mineral density scores that are significantly lower than those observed for age- and sex-matched normal subjects or those for nonhypercalciuric stone-forming patients. Most of these studies have relied on changes in bone mineral density and have not explored the mechanism(s) involved. There have been a small number of studies that have relied on dynamic bone histomorphometry to ascertain the nature of the bone defect in IH patients. When performed, these studies clearly have shown increased bone resorption and high bone turnover in patients with fasting hypercalciuria whereas suppressed bone formation indices are the most consistent finding in patients with the absorptive variant of IH. The causes of this apparent difference in bone remodeling between the 2 variants of IH still is uncertain. Available evidence suggests that potential mechanisms may be dependent in large part to genetic, metabolic, and nutritional causes of hypercalciuria and bone loss in patients with IH.

Reduced bone formation and relatively increased bone resorption in absorptive hypercalciuria

Absorptive hypercalciuria (AH), a common stone-forming condition characterized biochemically by intestinal hyperabsorption of calcium and hypercalciuria may be associated with bone loss. In AH type I (AH-1), hypercalciuria persists despite restriction in dietary calcium intake. We therefore hypothesized that the skeleton may contribute to the hypercalciuria in this subgroup of patients. Histomorphometric analysis of iliac crest biopsies were performed on nine stone-formers with AH-1 and on nine matched normal subjects. After stabilization on a stone-prevention diet, calcium homeostasis in the stone formers was then evaluated on inpatient constant metabolic diet before and after short-term blockade of bone resorption by alendronate (10 mg daily, 17 days total). Compared with controls, the stone-formers had lower indices of bone formation (osteoblast surface/bone surface 1.8+/-2.1 vs 3.0+/-1.5%, P=0.04; wall thickness 35.8+/-6.9 vs 47.2+/-7.6%, P=0.001) and relatively higher bone resorption (osteoclast surface/bone surface 0.4+/-0.2 vs 0.2+/-0.2%, P=0.05). In the stone-formers, a short-term course of alendronate treatment corrected fasting urinary calcium (0.14+/-0.06 to 0.06+/-0.04 mg Ca/mg Cr, P=0.001) and marginally reduced 24-h urinary calcium by 48 mg/day (P=0.06). Increased intestinal calcium absorption and hypercalciuria persisted, but estimated calcium balance improved (P=0.007). Our results suggest that the hypercalciuria of AH-1 originates primarily from intestinal hyperabsorption of calcium, but bone resorption in excess of bone formation may contribute.

Lithiasis and Risk Factors

Nephrolithiasis is a worldwide disease with high clinical and economic costs. The increasing incidence in industrialized countries seems to be related to several risk factors, which are partly inherited and partly acquired. Although risk factors in urolithiasis are still under discussion, their identification would provide a notable gain for the patient in terms of stone episodes, and for the health service in terms of costs. This article presents an easy classification of risk factors based on clinical background.