Benefits of omega-3 fatty acid against bone changes in salt-loaded rats: possible role of kidney.
There is evidence that dietary fats are important components contributing in bone health and that bone mineral density is inversely related to sodium intake. Salt loading is also known to impose negative effects on renal function. The present study aimed to determine the effect of the polyunsaturated fatty acid omega-3 on bone changes imposed by salt loading, highlighting the role of kidney as a potential mechanism involved in this effect. Male Wistar rats were divided into three groups: control group, salt-loaded group consuming 2% NaCl solution as drinking water for 8 weeks, and omega-3-treated salt-loaded group receiving 1 g/kg/day omega-3 by gavage with consumption of 2% NaCl solution for 8 weeks. Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and heart rate (HR) were recorded. Plasma levels of sodium, potassium, calcium, inorganic phosphorus (Pi), alkaline phosphatase (ALP), creatinine, urea, 1,25-dihydroxyvitamin D [1,25(OH)2D3], and transforming growth factor-beta1 (TGF-β1) were measured. The right tibia and kidney were removed for histologic examination and renal immunohistochemical analysis for endothelial nitric oxide synthase (eNOS) was performed. The results revealed that omega-3 reduced SBP, DBP, and MAP and plasma levels of sodium, potassium, Pi, creatinine, urea, and TGF-β1, but increased plasma levels of calcium, ALP, and 1,25(OH)2D3 as well as renal eNOS. Omega-3 increased cortical and trabecular bone thickness, decreased osteoclast number, and increased newly formed osteoid bone. Renal morphology was found preserved. In conclusion, omega-3 prevents the disturbed bone status imposed by salt loading. This osteoprotective effect is possibly mediated by attenuation of alterations in Ca(2+), Pi, and ALP, and improvement of renal function and arterial blood pressure.
The acquisition and maintenance of bone mass and strength are influenced by environmental factors, including physical activity and nutrition (Massey and Whiting 1996). Nutrition is important to bone health, and a number of minerals and vitamins have been identified as playing a potential role in the prevention of bone diseases, particularly osteoporosis (Massey and Whiting 1996). Evidence indicates that dietary fats can influence bone health (Tartibian et al. 2010), in particular the omega-3 (n-3) polyunsaturated fatty acids (PUFAs), as they have been shown to inhibit osteoclast activity and enhance osteoblast activity (Watkins et al. 2003). Eicosapentaenoic acid (EPA) supplementation was found to increase bone mineral density in postmenopausal women (Terano 2001). Beneficial effects of n-3 PUFAs on markers of bone resorption and formation in animal (Shen et al. 2006) and human (Griel et al. 2007) studies have, also, been observed.
On the other hand, a number of studies suggested a detrimental effect of dietary salt on bone. Devine et al. (1995) showed that change in bone mineral density was inversely related to sodium intake and that both dietary calcium and urinary sodium excretion were significant determinants of the change in bone mass. High-sodium diet was found to increase urinary calcium excretion and cause loss of bone calcium (Chan and Swaminathan 1998), while reducing sodium intake complemented the beneficial skeletal effects of the Dietary Approaches to Stop Hypertension diet (Lin et al. 2003). Furthermore, an epidemiological study of men and women has shown that salt intake is associated with markers of bone resorption and appears likely to be a risk factor for osteoporosis (Jones et al. 1997). Similar effect of sodium loading has been demonstrated in animal model (Gold and Gouldin 1995).