Lacidipine reduces high blood pressure and the target organ damage induced by high fructose diet in rats

Dietary sodium restriction prevents kidney damage in high fructose-fed rats

Sodium depletion has a protective effect on target-organ damage in hypertension independent of blood pressure. Here we tested whether chronic dietary sodium restriction may prevent the development of renal alterations associated with insulin resistance by reducing the inflammatory and oxidant state. Rats were fed normal-salt-60% fructose, low-salt-60% fructose, or control normal-salt diet for 12 weeks. Insulin resistance induced by high-fructose diet was associated with an increase in albuminuria, tubular and glomerular hypertrophy, and inflammation of kidney and adipose tissue. The low-salt diet improved insulin sensitivity and prevented kidney damage. These beneficial effects of sodium depletion were associated with a decrease in renal inflammation (macrophage infiltration, IL-6, TNF-α) and oxidative stress (NADPH oxidase activity), and a prevention of histologic changes in retroperitoneal fat induced by high fructose. Thus, dietary salt depletion has beneficial effects on renal and metabolic alterations associated with a high-fructose diet in rats.

Synergistic effect of uricase blockade plus physiological amounts of fructose-glucose on glomerular hypertension and oxidative stress in rats

Fructose in sweetened beverages (SB) increases the risk for metabolic and cardiorenal disorders, and these effects are in part mediated by a secondary increment in uric acid (UA). Rodents have an active uricase, thus requiring large doses of fructose to increase plasma UA and to induce metabolic syndrome and renal hemodynamic changes. We therefore hypothesized that the effects of fructose in rats might be enhanced in the setting of uricase inhibition. Four groups of male Sprague-Dawley rats (n = 7/group) were studied during 8 wk: water + vehicle (V), water + oxonic acid (OA; 750 mg/k BW), sweetened beverage (SB; 11% fructose-glucose combination) + V, and SB + OA. Systemic blood pressure, plasma UA, triglycerides (TG), glucose and insulin, glomerular hemodynamics, renal structural damage, renal cortex and liver UA, TG, markers of oxidative stress, mitDNA, fructokinase, and fatty liver synthase protein expressions were evaluated at the end of the experiment. Chronic hyperuricemia and SB induced features of the metabolic syndrome, including hypertension, hyperuricemia, hyperglycemia, and systemic and hepatic TG accumulation. OA alone also induced glomerular hypertension, and SB alone induced insulin resistance. SB + OA induced a combined phenotype including metabolic and renal alterations induced by SB or OA alone and in addition also acted synergistically on systemic and glomerular pressure, plasma glucose, hepatic TG, and oxidative stress. These findings explain why high concentrations of fructose are required to induce greater metabolic changes and renal disease in rats whereas humans, who lack uricase, appear to be much more sensitive to the effects of fructose.

The antioxidant tempol inhibits cardiac hypertrophy in the insulin-resistant GLUT4-deficient mouse in vivo

Reactive oxygen species such as superoxide are implicated in cardiac hypertrophy, but their contribution to the cardiac complications of insulin resistance is unresolved. We tested the hypothesis that the antioxidant tempol attenuates cardiac hypertrophy in insulin-resistant mice. Mice with cardiac GLUT4 deletion (GLUT4-knockout), superimposed on global GLUT4 suppression (GLUT4-knockdown) were administered tempol for 4 weeks. Age-matched GLUT4-knockdown littermates were used as controls (14 mice/group). GLUT4-knockout mice exhibited marked cardiac hypertrophy: heart to body weight ratio was increased 61+/-7% and expression of the hypertrophic genes beta-myosin heavy chain and B-type natriuretic peptide (BNP) were elevated 5.5+/-0.7- and 6.2+/-1.5-fold relative to control, respectively. Pro-fibrotic pro-collagen III expression was also higher (3.8+/-0.7-fold) in the GLUT4-knockout myocardium (all p<0.001). Both gp91(phox) and Nox1 subunits of NADPH oxidase were also upregulated, 4.9+/-1.2- and 9.3+/-2.8-fold (both p<0.01). Tempol treatment significantly attenuated all of these abnormalities in GLUT4-knockout mice. Heart to body weight ratio was decreased, as was fold expression of beta-myosin heavy chain (to 3.8+/-0.8), BNP (to 2.5+/-0.5), pro-collagen III (to 1.9+/-0.4), gp91(phox) (to 0.9+/-0.3) and Nox1 (to 2.3+/-0.1, all p<0.05 versus untreated GLUT4-knockout mice). In addition, tempol upregulated ventricular expression of both thioredoxin-2 (confirming an antioxidant action) and glycogen synthase kinase-3beta (GSK-3beta). Tempol did not elicit any other significant changes in control mice. Cardiac superoxide generation, however, was not altered by GLUT4-knockout or tempol. In conclusion, tempol treatment reduced morphological and molecular evidence of cardiac hypertrophy in the GLUT4-knockout insulin-resistant mouse in vivo, even at doses insufficient to lower cardiac superoxide. Parallel reductions in pro-collagen III and NADPH oxidase have important implications for our understanding of the molecular basis of cardiac hypertrophy in the setting of insulin resistance. Antioxidants may offer new alternatives in this disorder.

Antihypertensive Treatment and Renal Damage

Besides generating renal damage, hypertension plays an important role in the progression of diabetic nephropathy. The fructose-fed rat is a well-established model both of high blood pressure and renal impairment, which is similar to diabetic nephropathy. To clarify the relationship between hypertension, glucose metabolism, and kidney remodeling, we investigated the renal level of Glut 1 and Glut 5, their relation to fibrosis and the effects of an antihypertensive drug on renal damage. Twenty-four male WK rats were divided into three groups: 8 animals received a fructose-enriched diet, 8 a control diet, and 8 animals a high-fructose diet plus amlodipine (5 mg/Kg). After six weeks of treatment, we observed a significant increase in Glut 5, fibronectin, and sorbitol in fructose-fed rats compared with control and amlodipine-treated animals; there was a positive correlation between Glut 5 and fibronectin levels (r = 0.63). Glut 1 levels were similar in all three groups, whereas collagen IV was higher in fructose-fed rats; amlodipine prevented the increase of collagen IV and sorbitol. Collagen I was statistically higher in the fructose group than in the other two groups. Therefore, prolonged fructose feeding results in renal fibrosis via polyol pathway overactivity that can be prevented by means of an antihypertensive drug.

Lacidipine

Lacidipine (Caldine, Lacimen, Lacipil, Midotens, Motens) is a once-daily, orally-administered, lipophilic dihydropyridine calcium antagonist with an intrinsically slow onset of activity, resulting in a lack of reflex tachycardia. It has a long duration of action and a high degree of vascular selectivity. In addition to calcium channel-modulated vasodilation, lacidipine displays antioxidant activity greater than that of other dihydropyridine calcium antagonists. In randomised, well-controlled trials, lacidipine 2-6 mg orally once daily had antihypertensive efficacy similar to that of other long-acting dihydropyridine calcium antagonists, thiazide diuretics, atenolol (a beta-blocker) and enalapril (an ACE inhibitor). Lacidipine was effective in elderly patients (including those with isolated systolic hypertension), African Nigerian patients and patients with concurrent type 2 diabetes mellitus. During long-term treatment for 4 or 5 years in patients with isolated systolic hypertension or essential hypertension, the incidence of cardiovascular events and mortality with lacidipine was similar to that with chlorthalidone or atenolol. The European Lacidipine Study on Atherosclerosis (ELSA), in which 2334 patients with hypertension were randomised to 4 years of therapy with lacidipine 4-6 mg/day or the beta-blocker atenolol 50-100 mg/day, demonstrated significantly lower atherosclerotic progression and plaque formation with lacidipine compared with atenolol in patients completing the full 4 years of the study. Between-group differences in favour of lacidipine for the primary efficacy variable (mean change in carotid artery intima-media thickness) did not reach statistical significance in the intent-to-treat population. The tolerability profile of lacidipine (headache, flushing, pedal oedema, dizziness and palpitations) is similar to that of other dihydropyridine calcium antagonists, but with a lower incidence of peripheral oedema. Data from the ELSA study suggest that the incidence of serious adverse events during long-term lacidipine therapy is similar to that with atenolol.

CONCLUSION

Lacidipine is an effective, well tolerated, once-daily, oral antihypertensive agent that can be used in a wide variety of patients. As with other members of its class, lacidipine has shown potentially beneficial antiatherosclerotic effects, although definitive data with respect to possible superiority over other drug classes are still required. Therefore, lacidipine is an attractive therapy for the long-term management of essential hypertension.

Antihypertensive treatment with enrasentan (SB217242) in an animal model of hypertension and hyperinsulinemia

Enrasentan is an antagonist of endothelin (ET) receptors. Previous studies have shown that antagonism of ET receptors might represent a new approach to the treatment of hypertension. Rats with a high-fructose diet (HFD) develop hyperinsulinemia, hypertriglyceridemia, and hypertension; renal and cardiac damage. The aim of this study was to evaluate whether enrasentan could reverse the hypertension and reduce the target organ damage induced by an HFD. Fifty-five WKY rats were divided into 6 groups; 35 animals received HFD for a month; thereafter 5 animals were killed, and the others were treated either with enrasentan (n = 10), hydralazine (n = 10), or placebo (n = 10) for a further month while on the HFD. Twenty animals were kept on a standard diet throughout the study; either placebo (n = 10) or enrasentan (n = 10) was administered during the second month. Enrasentan and hydralazine completely eliminated the HFD-induced increase in blood pressure; however, only enrasentan reduced the renal and cardiac damage caused by the diet. In conclusion, enrasentan was effective both in normalizing blood pressure and in reducing renal and cardiac damage; the organ protection cannot be attributed solely to the antihypertensive effect, because it was absent in the case of hydralazine, despite successful control of blood pressure.

New Insights into the Therapeutic Mechanism of Action of Calcium Channel Blockers in Salt-Dependent Hypertension: Their Interaction with Endothelin Gene Expression

It appears that the beneficial action of calcium channel blockers (CCBs) in hypertension may be related to short-term and long-term effects. This paper summarises pharmacological studies aiming to characterise those effects. The primary consequence of the short-term effects is the decrease of blood pressure related to a selective interaction of CCBs with calcium channels in hypertensive vessels. The long-term effects may additionally control the disease through prevention of end organ damage, accompanying the interaction of CCBs with the pathways, leading to the re-expression of embryonic genes and to the overactivation of type I collagen gene, which are amplified by a high-salt diet. ET-1 and tumour growth factor beta-1 could be among the main factors activating those pathways. The processes leading to overexpression of those factors and to tissue remodelling may be controlled by lacidipine, independent of the reduction of blood pressure.

Bosentan reduces blood pressure and the target-organ damage induced by a high-fructose diet in rats

BACKGROUND

Rats fed a high-fructose diet develop hyperinsulinaemia, hypertriglyceridaemia, hypertension, renal changes similar to those in diabetic rats and left ventricular hypertrophy with deposition of collagen. Bosentan is an antagonist of endothelin receptors. Other authors have demonstrated that bosentan is effective in preventing the increase in blood pressure induced by a high-fructose diet but, until now, the effect of the drug on the target organs has not been investigated.

OBJECTIVE

To evaluate whether bosentan is effective, not only in reducing blood pressure, but also in limiting the renal and cardiac changes induced by a high-fructose diet

METHODS

Forty Wistar-Kyoto (WKY) male rats were divided into four groups: groups 1 and 2 received a high-fructose diet, groups 3 and 4 received a standard diet for 1 month. Thereafter, the following treatments were administered: group 1, high-fructose diet plus bosentan 100 mg/kg per day; group 2, high-fructose diet plus placebo; group 3, standard diet plus bosentan 100 mg/kg per day; group 4, standard diet plus placebo. After a further 1 month, all animals were killed. A morphometric analysis was performed by examining 100 glomeruli for each animal. Renal deposits of collagen and fibronectin and cardiac deposits of collagen III were measured by means of immunochemistry.

RESULTS

By the end of the study, bosentan had completely reversed the increase in blood pressure induced by a high-fructose diet, without modifying the blood pressure in normotensive rats. Moreover, bosentan reduced glomerular hypertrophy and deposits of collagen and fibronectin in the kidney and cardiac deposits of collagen III.

CONCLUSIONS

The results of this study demonstrate that bosentan not only normalizes blood pressure, but also protects target organs in rats receiving a high-fructose diet.