Summary 255 Research Summary

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1 Chapter 10 Summary Nephrolithiasis remains a public health problem around the world, affecting 12% of the adult population. The prevalence and incidence of kidney stones are increasing with global warming, reduced water intake and affluent diet. Chemical analysis shows that calcium oxalate stones are the most common type of kidney stones. A careful history reveals a number of dietary and lifestyle risk factors contributing to an individual s risk of stone disease. The current strategies available for the management of kidney stones are inefficient, costly and associated with severe adverse effects some even leading to mortality. There is also a dearth of information on the pathogenesis of kidney stone formation. Hence development of drugs for nephrolithiasis has been the focus of many research concerns. Studies on animal models have provided the evidence for the involvement of reactive oxygen species, the subsequent oxidative stress and depletion of antioxidant enzymes in calcium oxalate induced nephrolithiasis. Hence the use of antioxidants for the treatment and management of nephrolithiasis has been of medical interest. Astaxanthin has invited the attention of current biological research owing to its high antioxidant potential surpassing all known antioxidants. The possibility of use of astaxanthin in oxidative stress diseases has generated great interest in clinical trials and increased the production of astaxanthin at commercial levels. Furthermore it is used as a nutritional supplement and has no side effects have been reported so far. In this study, astaxanthin extracted from H. pluvialis microalgae was analysed for its beneficial effect on rodent models of calcium oxalate nephrolithiasis.

2 252 Two doses of astaxanthin, 25 mg/kg b.wt. and 50 mg/kg b.wt., were used for the study. There was a reduction in the food and water intake and urine volume in the nephrolithiatic rats which was increased to normal levels by astaxanthin administration. The reduction in body weight and increase in the relative liver and kidney weights in the nephrolithiatic animals were also restored to normal in the astaxanthin treated animals. This pointed out to a possible protective effect of astaxanthin administration in nephrolithiatic animals by stimulating diuresis and preserving the integrity of the renal and hepatic tissues. Renal function markers were assessed and it was found that the nephrolithiatic animals had a reduced renal function, low GFR and increased levels of the tubular brush border enzymes NAG and AAP. The liver function markers were monitored and found to be significantly elevated in the nephrolithiatic animals. Lipid peroxidation was increased and the levels of SOD, catalase, GPx, GST, GR, GSH and the vitamins C and E were reduced in the liver and kidney tissues of the nephrolithiatic animals. The levels of the renal function markers were brought to normal and the tubular brush border enzyme levels were reduced on astaxanthin treatment. This implicated that astaxanthin is able to reduce damage to renal tubules and promote elimination of waste products by increasing the GFR. This protective effect may be due to the diuretic effect observed in the study and its superior antioxidant effect. Astaxanthin treatment reduced the extent of lipid peroxidation and restored the levels of the antioxidants in the liver as well as in the renal tissue which supported the above observation. Astaxanthin was also beneficial in restoring the liver function in these animals indicating that it exerts no hepatotoxicity at the doses used in the study. The examination of the histology of the renal tissue of the nephrolithiatic animals by H & E staining showed numerous crystal depositions in the lumen of the renal tubules. Tubular damage score revealed an increased extent of tubular

3 Summary 253 damage which occurred due to crystal deposition. Pizzolato staining confirmed these crystals to be calcium oxalate. The kidney of the nephrolithiatic animals had a high content of calcium as measured by flame photometry. The SEM- EDX analysis also helped to validate these observations. Astaxanthin administration reduced the calcium deposition and reduced the renal tubular damage. The calcium content of the renal tissue of the astaxanthin treated animals were close to the control values. Very few or no crystals were observed in the renal tissue of the astaxanthin treated animals indicating the ability of astaxanthin to reduce calcium oxalte crystal formation. Proteins are found as major components in human renal stone matrix and are considered to have a potential role in crystal membrane interaction, crystal growth and stone formation. In the current investigation, the expression of the major stone matrix protein OPN was studied. OPN was found to be upregulated in the renal tissue of the nephrolithiatic animals as evidenced by immunohistochemical staining and RT-PCR studies. The analysis of kidney of the astaxanthin treated animals showed a reduction in OPN expression and little or absence of OPN protein in the renal tissue. To find an insight into the possible mechanism of action of astaxanthin in addition to its antioxidant effect, the role of the renal RAS was considered. The measurement of renal and urinary ACE, an integral component of the RAS system, showed that these were increased in the nephrolithiatic animals and reduced in astaxanthin treated animals. This pointed out to the possibility of an ACE inhibitory activity of astaxanthin. Reactive oxygen species mediated reactions trigger the up regulation of cytokines like TGF-β1 through RAS. To find a link between oxidative stress and OPN upregulation, the expression of TGF-β1 was also studied by RT-PCR in the kidney tissue. TGF-β1 was upregulated in the nephrolithiatic rat kidneys and was not observed in the kidney of the astaxanthin treated animals. This implicated

4 254 that oxidative stress conditions trigger the production of TGF-β1 by stimulating the RAS system. The ACE enzyme converts angiotensin I into angiotensin II which might in turn cause the TGF-β1 production. TGF-β1 is a known stimulator of OPN production. Increased OPN in renal tissues promote crystal cell adhesion and adherence to renal epithelial cells. The mechanism by which astaxanthin exerts its antilithiatic effect may also be by its ability to reduce the ACE levels thereby reducing TGF-β1 and OPN production. This would result in crystal dissolution and resist further crystal formation in the renal tubules. Thus the RAS modulatory effect of astaxanthin along with its antioxidant activity may account for its protective effect on calcium oxalate nephrolithiasis. The present clinical strategy for kidney stones is to give citrate supplementation usually as potassium citrate. Hence, animals were treated with potassium citrate for the two durations used in our study. They were assessed for all the parameters considered in the study with a view to compare the present treatment with astaxanthin treatment. There was only a marginal improvement in renal and liver functions on potassium citrate treatment. It also failed to alleviate the oxidative stress in the liver and kidney tissue to the extent as astaxanthin. The OPN and TGF-β1 expressions and ACE levels were higher than in the renal tissue of the potassium citrate treated animals than in the astaxanthin treated animals. Hence the treatment with astaxanthin was found to be more effective than the potassium citrate therapy used in the clinical management of kidney stones at both the tested durations. When all the parameters were taken into account, the dose of 50 mg/kg b.wt. of astaxanthin administered for 42 days showed maximum effect among the doses used in this study. Astaxanthin is available in the market as a nutraceutical and it is reported to have no adverse effects. The prospect of using a natural product in clinical management of nephrolithiasis offers much promise in cutting down the

5 Summary 255 expenditure involved in the surgical removal of kidney stones. Thus it is also a cost effective strategy for the treatment of kidney stones. However, additional clinical trials are necessary to evaluate its prophylaxis in nephrolithiasis. On the basis of the present study, investigations can be carried out to elucidate the mechanism of ACE inhibition of astaxanthin. The effect of astaxanthin on other stone matrix proteins can also be assessed. With the development of advanced techniques in molecular biology, more research can be carried out to study the exact mechanism by which astaxanthin exerts its membrane protective effect and antioxidant activity. Research Summary