Membrane injury facilitated the fixation of calcium oxalate crystals and subsequent growth into kidney stones. Oxalate-induced membrane injury was mediated by lipid peroxidation reaction through the generation of oxygen free radicals. In urolithic rat kidney or oxalate exposed cultured cells, both superoxide anion and hydroxyl radicals were generated in excess, causing cellular injury. In hyperoxaluric rat kidney, both superoxide and H2O2-generating enzymes such as glycolic acid oxidase (GAO) and xanthine oxidase (XO) were increased, and hydroxyl radical and transition metal ions, iron, and copper were accumulated. The lipid peroxidation products, thiobarbituric acid-reactive substances (TBARS), hydroperoxides, and diene conjugates were excessively released in tissues of urolithic rats and in plasma of rats as well as stone patients. The accumulation of these products was concomitant with the decrease in the antioxidant enzymes, superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), and glucose-6 phosphate dehydrogenase (G6PD) as well as radical scavengers, vitamin E, ascorbic acid, reduced glutathione (GSH), and protein thiol. All the above parameters were decreased in urolithic condition, irrespective of the agents used for the induction of urolithiasis. Oxalate binding activity and calcium oxalate crystal deposition were markedly pronounced, along with decreased adenosine triphosphatase (ATPase) activity. Lipid peroxidation positively correlated with cellular oxalate, oxalate binding, gamma-glutamyl carboxylase, and calcium level and negatively correlated with GSH, vitamin E. ascorbic acid, and total protein thiol. Antioxidant therapy to urolithic rats with vitamin E, glutathione monoester, methionine, lipoic acid, or fish oil normalised the cellular antioxidant system, enzymes and scavengers, and interrupted membrane lipid and protein peroxidation reaction, ATPase inactivation, and its associated calcium accumulation. Antioxidant therapy prevented calcium oxalate precipitation in the rat kidney and reduced oxalate excretion in stone patients. Similarly, calcium oxalate crystal deposition in vitro to urothelium was prevented by free radical scavengers such as phytic acid and mannitol by protecting the membrane from free radical-mediated damage. All these observations were suggestive of the active involvement of free radical-mediated lipid peroxidation-induced membrane damage in the pathogenesis of calcium oxalate crystal deposition and retention.

Calcium oxalate stone disease: role of lipid peroxidation and antioxidants.

Recent animal work suggests that gamma-linolenic acid (GLA) and eicosapentaenoic acid (EPA) enhance calcium absorption, reduce excretion and increase calcium deposition in bone. A pilot study was set up to test the interactions between calcium and GLA+EPA in humans. Sixty-five women (mean age 79.5), taking a background diet low in calcium, were randomly assigned to GLA+EPA or coconut oil placebo capsules; in addition, all received 600 mg/day calcium as the carbonate. Markers of bone formation/degradation and bone mineral density (BMD) were measured at baseline, 6, 12 and 18 months. Twenty-one patients were continued on treatment for a second period of 18 months, after which BMD (36 months) was measured. At 18 months, osteocalcin and deoxypyridinoline levels fell significantly in both groups, indicating a decrease in bone turnover, whereas bone specific alkaline phosphatase rose indicating beneficial effects of calcium given to all the patients. Lumbar and femoral BMD, in contrast, showed different effects in the two groups. Over the first 18 months, lumbar spine density remained the same in the treatment group, but decreased 3.2% in the placebo group. Femoral bone density increased 1.3% in the treatment group, but decreased 2.1% in the placebo group. During the second period of 18 months with all patients now on active treatment, lumbar spine density increased 3.1% in patients who remained on active treatment, and 2.3% in patients who switched from placebo to active treatment; femoral BMD in the latter group showed an increase of 4.7%. This pilot controlled study suggests that GLA and EPA have beneficial effects on bone in this group of elderly patients, and that they are safe to administer for prolonged periods of time.

Calcium, Gamma-Linolenic Acid and Eicosapentaenoic Acid Supplementation in Senile Osteoporosis

Calcium metabolism, osteoporsis and essential fatty acids: A review

Current examples for the development of urinary stone disease are discussed by means of data from the literature and our own studies. Urinary stone disease has gained increasing significance due to changes in living conditions, i.e., industrialization and malnutrition. Changes in prevalence and incidence, the occurrence of stone types and stone location, and the manner of stone removal are explained. The importance of nutrition in the prevention of calcium oxalate stone disease is discussed in terms of fluid intake, calcium and oxalate metabolism, and dietary fat intake. The results of a study on a standardized mixed diet or an ovo-lactovegetarian diet show that well-balanced nutrition with consecutive high intake of fluids leads to a significant decrease in the risk for urinary stone formation (calculated as relative supersaturation with calcium oxalate by the computer program EQUIL).

Current aspects of epidemiology and nutrition in urinary stone disease.

Eicosapentaenoic acid (EPA), one of the polyunsaturated fatty acids, is well-known to have a wide variety of beneficial biological functions. In the present work we demonstrate another new beneficial effect of EPA on bone metabolism in vivo. Ovariectomized rats were divided into 4 groups under the same calorie intake condition; (1) normal diet, (2) low calcium diet (1.5mg/day), (3) EPA-enriched diet (160mg/day/kg), (4) EPA-enriched and low calcium diet. These diets were continued for 35 consecutive days. The bone weight of the femora and tibiae decreased significantly in the low calcium group, but the decrease was inhibited in the EPA-low calcium group. Moreover, in the rupture test, which indicates bone strength, the femora in the low calcium group were easier to break than in the normal calcium diet groups. In the EPA-low calcium group the strength of the bone was equivalent to that in the normal diet group. These results suggest that an EPA-enriched diet prevents the loss of bone weight and strength caused by oestrogen deficiency or inadequate nutrition. There is a possibility that EPA could be developed to be a novel anti-osteoporosis drug.

A. Colin Buck

Papers

The protective role of eicosapentaenoic acid [EPA] in the pathogenesis of nephrolithiasis