Toxicol Appl Pharmacol. 2007 Jun 21; : 17658574 PubMed

Mitochondrial impairment by PPAR agonists and statins identified via immunocaptured OXPHOS complex activities and respiration.

MitoSciences, Inc., 1850 Millrace Drive, Eugene, OR 97403, USA
Sashi Nadanaciva , James A Dykens , Autumn Bernal , Roderick A Capaldi , Yvonne Will

Mitochondrial impairment is increasingly implicated in the etiology of toxicity caused by some thiazolidinediones, fibrates, and statins. We examined the effects of members of these drug classes on respiration of isolated rat liver mitochondria using a phosphorescent oxygen sensitive probe and on the activity of individual oxidative phosphorylation (OXPHOS) complexes using a recently developed immunocapture technique. Of the six thiazolidinediones examined, ciglitazone, troglitazone, and darglitazone potently disrupted mitochondrial respiration. In accord with these data, ciglitazone and troglitazone were also potent inhibitors of Complexes II+III, IV, and V, while darglitazone predominantly inhibited Complex IV. Of the six statins evaluated, lovastatin, simvastatin, and cerivastatin impaired mitochondrial respiration the most, with simvastatin and lovastatin impairing multiple OXPHOS Complexes. Within the class of fibrates, gemfibrozil more potently impaired respiration than fenofibrate, clofibrate, or ciprofibrate. Gemfibrozil only modestly inhibited Complex I, fenofibrate inhibited Complexes I, II+III, and V, and clofibrate inhibited Complex V. Our findings with the two complementary methods indicate that (1) some members of each class impair mitochondrial respiration, whereas others have little or no effect, and (2) the rank order of mitochondrial impairment accords with clinical adverse events observed with these drugs. Since the statins are frequently co-prescribed with the fibrates or thiazolidinediones, various combinations of these three drug classes were also analyzed for their mitochondrial effects. In several cases, the combination additively uncoupled or inhibited respiration, suggesting that some combinations are more likely to yield clinically relevant drug-induced mitochondrial side effects than others.

and useful for me. Thank you.

I see that atorvastatin is missing in this study. Given the huge push right now in doctor's offices, I'd like to know it relative status.

I appreciate your posts with studies like this!

the web site of the company for whom the authors work is quite interesting:
http://www.mitosciences.com/parkinsons.html

Seems to be at odds with the study in this thread:

http://neurotalk.psychcentral.com/sh...ighlight=zocor

In the study first mentioned, only one specific statin, simvastatin, reduced the risk of PD by 50%, and they suggested it may be because it enters the brain easily. Other statins like Lipitor did not do the trick.

I've been taking zocor (simvastatin) for a few years.

"The researchers speculate that the selective benefit observed with simvastatin might be due to the combination of high potency and the ability to enter the brain."

simvastatin has been found to be the most lipophilic of the statins, and thus crosses the blood brain barrier easiest, and pravastatin the least (pravastatin is hydrophilic). atorvastatin (lipitor) is thought to be intermediate in ability to cross the BBB, but all the lipophiic statins (fat soluble ones) are found in the cerebral spinal fluid, and thus theorized to cross the BBB.
there is no question that statins are great anti-inflammatory agents and increase perfusion everywhere--the other "pleiotropic" effects are of concern to me. statins interfere with the mevalonate pathway, many steps removed from its effect upon cholesterol.

http://www.cholesterol-and-health.co...olesterol.html

I found it looking around the net today.

The "pleiotropic" effects of statins are why I love them. They reduce inflammation of the arterial walls, and may increase bone density, too.

"These agents appear to reduce bone fractures and may improve insulin sensitivity and reduce the likelihood of persons progressing from impaired glucose tolerance to type II diabetes. "

Pleiotropic Effects of Statins: Lipid Reduction and Beyond
S. I. McFarlane, R. Muniyappa, R. Francisco and J. R. Sowers

Abstract

There is accumulating evidence that statins have beneficial effects that are independent of their classical actions on lipoproteins. These effects include reductions in inflammation in the vasculature, kidney, and bone. Potential beneficial effects of these agents include enhancement of nitric oxide production in vasculature and the kidney. These agents appear to reduce bone fractures and may improve insulin sensitivity and reduce the likelihood of persons progressing from impaired glucose tolerance to type II diabetes. Potential beneficial pleiotropic effects of statins are covered in this review.

THE 3-HYDROXY-3-METHYLGLUTARYL COENZYME A (HMG-CoA) reductase inhibitors (statins) have multiple actions above and beyond that of cholesterol lowering. These pleiotropic actions include direct effects on vascular tissue, kidney, bone, and glucose metabolism. Clinical trials and animal studies (in vivo and in vitro) have shown that these agents reduce cardiovascular disease (CVD) risks and events (1, 2, 3), progression of nephropathy (4), development of diabetes (5), and fracture rates (6); these are benefits that go beyond lipid lowering alone. Potential beneficial effects are due to the positive impact on vascular and glomerular nitric oxide (NO) production and attenuation of vascular inflammation. Effects on bone, including fracture reduction, are thought to be mediated by direct action on bone formation. Finally, potential reduction in the development of diabetes as observed in the West of Scotland Coronary Prevention Study (WOSCOPS) (5) may relate to the improvement in insulin sensitivity. Actions of statins on vascular, glomerular, bone, and insulin-sensitive tissue will be discussed in this review.

Impact on CVD

Statins have been shown in primary (1, 2) and secondary prevention (3, 7, 8) trials to significantly reduce fatal and nonfatal CVD events. Cardiovascular benefits of statins have been conventionally attributed to reduction of LDL-cholesterol (9). However, subanalyses of large clinical trials suggest that statins also have direct cardioprotective effects. For example, in WOSCOPS (1), the time-to-event curves began to diverge within 6 months of initiating therapy, an effect that is earlier than predicted from cholesterol lowering alone. Clinical trials have also shown larger significant CVD benefits associated with only minimal changes in luminal dimensions on angiography, benefits that cannot be explained by simple plaque regression (10). Statins also increase myocardial perfusion and reduce recurrent anginal episodes after acute coronary events (11). Potential mechanisms that may mediate these effects include modulation of endothelial function, plaque stabilization, attenuated atherogenesis, and anti-inflammatory and antithrombotic action.

Statins and plaque stabilization.

Most acute coronary events are due to disruption of unstable atherosclerotic plaques, which result in thrombotic occlusion. These vulnerable lesions occur in moderately stenotic vessels and are characterized by a lipid-rich core and excess activated inflammatory cells (12). Macrophages release matrix metalloproteases that degrade plaque matrix connective tissue, weaken the fibrous cap, and render them susceptible for rupture (12). Statins have been shown to decrease the levels of metalloproteases, oxidized-LDL (ox-LDL), core lipid content, and macrophages and to increase collagen content in plaque matrix, actions that increase plaque stability (13).

Statins and endothelial function.

Statins have beneficial effects on vascular endothelium (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27), and many of these effects are mediated by the inhibition of small molecular weight G-proteins of the Ras superfamily (Ras and Rho). These small molecular weight G-proteins are involved in cell proliferation, differentiation, apoptosis, migration, contraction, and regulation of gene transcription. Activated Ras/Rho proteins are key components in signal-transducing kinase cascades involved in NO production and glucose metabolism. Thus, inhibition of these proteins can critically affect various cellular processes. The anchoring of these small G-proteins to cell membranes requires prenylation; Ras proteins are farnesylated, whereas Rho proteins are geranylgeranylated. Small G-proteins exist in an inactive GDP-bound cytosolic form, and upon cellular activation they exchange GTP and translocate to the active-membrane form (Fig. 1Go). Lack of protein isoprenylation leads to cytosolic sequestration and loss of biological activity. Statins, in addition to lowering cholesterol by inhibiting HMG-CoA reductase enzyme, also reduce cellular isoprenoid intermediates such as dolichol, ubiquinone, farnesol, and geranylgeraniol (Fig. 2Go). Statins, by inhibiting isoprenylation, effectively lower membrane levels and activity of Ras/Rho proteins and thus improve vascular function.



Studies in humans and animals have demonstrated a positive effect of statins on endothelial function. Basal and stimulated endothelium-dependent forearm blood flow responses in hypercholesterolemic subjects are improved in 4 wk of treatment with statin (14). Simvastatin has been reported to increase endothelial NO production and improve NO-dependent vasorelaxation in different vascular beds (15, 16). Chronic administration of simvastatin or mevastatin to rodents up-regulates endothelial NO synthase (eNOS) expression (17, 18), augments blood flow in cerebral vessels, and reduces infarct size (18). These studies suggest a direct action of the statins on NO production in the endothelium. Nevertheless, a major mechanism of action of statins in improving endothelial-derived vasorelaxation is through LDL-cholesterol lowering. Indeed, acute lowering of LDL by apheresis has been shown to improve endothelium-dependent vasodilatation in persons with hypercholesterolemia (19).

eNOS resides in the caveolae and produces small amounts of NO on demand in a transient fashion that is both calcium- and calmodulin-dependent. In the caveolae, eNOS is bound to the caveolar protein, caveolin that inhibits its activity. Elevations in cytoplasmic calcium promote binding of calmodulin to eNOS that subsequently displaces caveolin, thus activating eNOS (Fig. 3Go). In addition to undergoing regulatory posttranslational modifications, eNOS is regulated by a serine-threonine kinase, Akt. Akt is activated by insulin/IGF-I binding to endothelial and vascular smooth muscle cells (VSMCs) (20). Phosphorylation by Akt increases the affinity of eNOS to calmodulin and enhances the activity of eNOS. Statins activate Akt and thus increase NO production (21). Statins also decrease cellular caveolin levels and attenuate the inhibition of eNOS by caveolin, resulting in increased NO production (22). In addition to affecting posttranslational regulatory mechanisms, statins increase eNOS transcription, stability, and protein level (23). These class effects of statins contribute to improved NO-mediated vascular relaxation.

Endothelial dysfunction is a hallmark of diabetes and insulin-resistant states and is characterized by reduced effective vascular NO action (20). Statins ameliorate the abnormal vascular relaxation and partially restore NO production in the aorta of diabetic mice (24). Hyperglycemic states both in vivo and in vitro stimulate Rho activity (25), which in turn activates Rho-kinase resulting in increased vascular tone. The protective effect of statins on diabetic vascular disease may be due to the suppression of Rho kinase cascades, resulting in increased NO production and decreased vascular tone. Statins not only increase endothelial cell NO production but also up-regulate the inducible form of NOS (iNOS) in VSMCs (26). iNOS is expressed after vascular injury, and induction of iNOS in these states may be beneficial in preventing restenosis.

Statins also modulate the release and action of vasoconstrictors (e.g. endothelin and angiotensin II) (27, 28). Clinical studies show that hypercholesterolemic men have exaggerated hypertensive responses to infused Ang II, and this response is reversed by statins (29). In a study using double transgenic rat model harboring the human renin and angiotensin genes, cervistatin improved survival, decreased blood pressure, and reduced cardiac hypertrophy (30). Statins also have a direct effect on endothelin-1 (ET-1) production (Fig. 3Go). These agents reduce, in a dose- and time-dependent fashion, the expression of ET-1 in endothelial cells. This reduction is maintained even in the presence of ox-LDL (27). Because ET-1 is a powerful vasoconstrictor, decreasing ET-1 levels potentially reduces vascular resistance and improves blood flow in coronary and systemic vascular beds.

The anti-inflammatory actions of statins.

The vascular inflammatory response is a complex process that leads to thrombus formation, angiogenesis, neointimal thickening, and atherosclerosis (12). Markers of inflammation such as C-reactive protein, IL-6, TNF-{alpha}, and monocyte-chemotactic protein-1 (MCP-1) have, in varying degrees, been proposed as CVD risk factors (12). Recent evidence indicates that statins decrease C-reactive protein levels in just 6 wk of treatment, independent of LDL cholesterol reduction, and suggests that statins possess anti-inflammatory actions (31, 32).

Augmented expression of adhesion molecules on leukocytes (e.g. CD11b) and endothelial cells (e.g. P-selectin, intracellular adhesion molecule, ICAM-1) is necessary and critical in the early vascular response to injury. Cytokines, in addition to enhancing cellular adhesion, promote chemotaxis and stimulate vascular proliferation. Statins affect many of these events in the inflammatory cascade by inhibiting receptor-dependent activation of signal-transducing cascades. In a rat model of coronary inflammation, pravastatin reduces MCP-1 expression, monocyte infiltration, and proliferation (33). Simvastatin reduces leukocyte rolling, adherence, and transmigration in a rodent model of NO deficiency and attenuates endothelial adhesion molecule (34) and monocyte CD11b expression (35) in the absence of lipid lowering (Fig. 4Go). Statin therapy reduced the levels of soluble P-selectin in patients with acute coronary syndromes (36). In another rat model associated with elevated serum levels of TNF-{alpha} and IL-1ß, cerivastatin has been shown to reduce serum levels of these markers and improve survival rate (37). Statins also mediate the suppression of cytokine and adhesion molecule expression by reducing NF-{kappa}B activity in inflammatory and vascular cells (33). These observations underlie the importance of statins in attenuating the inflammatory process and the consequent impact on CVD risk reduction.

continued:

Statins and oxidative stress.

Oxidative stress is a result of altered balance in the relative concentrations of oxidants and antioxidants. Ox-LDL is deleterious to endothelial and VSMCs; it activates macrophages, induces release of various cytokines, and increases endothelial adhesiveness resulting in vascular injury and inflammation. Statins as potent antioxidants and antiatherosclerotic agents are attractive therapeutic options for preserving normal vascular function and blood flow. In several human and animal studies, various statins have been shown to: 1) inhibit the uptake and generation of ox-LDL (38), 2) attenuate vascular and endothelial superoxide anion formation by inhibition of NADH oxidases via Rho-dependent mechanisms (39, 40); and 3) preserve the relative levels of vitamin E, vitamin C, and endogenous antioxidants such as ubiquinone and glutatione in LDL particles (41, 42, 43). Thus, statins not only decrease oxidants but also restore antioxidants, thereby possibly reducing the level of oxidative stress in the vascular milieu, which may explain some of the observed clinical beneficial effects.

Statins and thrombosis.

Statins have been shown to play a role in altering the levels of several key elements in the process of thrombosis. Different statins have varying effects on prothrombotic factors, such as tissue factor, tissue factor pathway inhibitor, platelet aggregation, blood and plasma viscosity, fibrinogen, plasminogen activator inhibitor 1 (PAI-1), and lipoprotein (a) (44). Cellular expression of tissue factor in human macrophages is suppressed by lipophilic statins (45). Statins normalize thrombin generation in hypercholesterolemic patients and reduce platelet aggregation (46). Furthermore, decreases in platelet aggregation after statin therapy may be partially related to relative reductions in the cholesterol to phospholipid content in the platelet membrane (47).

Elevated fibrinogen levels and plasma viscosity may contribute to increased risk for CVD events in patients with and without established coronary artery disease (20, 46). Conflicting results exist on the effects of statins on fibrinogen levels and blood viscosity (48, 49, 50). Elevated plasminogen activator inhibitor 1 levels are associated with prothrombotic states, and statins reduce these levels (51); however, this effect is not a class effect. Further studies are needed to explain the apparent conflicting results.

Statins and vasculogenesis.

Statins, in addition to modulating endothelial and vascular function, may mediate neovascularization (vasculogenesis) and collectively contribute to the reduction in recurrent CVD events. Increased vasculogenesis has been demonstrated in rabbits treated with simvastatin via the activation of vascular Akt (21). Statins mobilize endothelial progenitor cells (EPCs) from the bone marrow that play a role in maintenance vasculogenesis (52). Increased EPCs are seen immediately after a coronary event (53) and line the endothelium of myocardial vessels (54). Indeed, statin therapy is associated with enhanced EPCs in patients with coronary artery disease (55).

Statins and kidneys

Statins have been shown to attenuate renal injury in both in vivo and in vitro studies. Renal injury initiates inflammatory cascades that involve similar cellular events as seen in vascular tissue. Statins inhibit key events in this process that alter the progression of renal injury. In hyperglycemic insulin-deficient diabetic rats, pravastatin ameliorates the structural and functional changes of diabetic nephropathy (56). Although the pathogenesis of diabetic nephropathy is complex and multifactorial, statins have been demonstrated to decrease TGF-ß production and suppress the enhanced Ras-dependent activation of MAPK cascade (Fig. 4Go). Lovastatin has similar action on glomerular disease in obese insulin-resistant rats (57). In another model of renal injury due to overexpression of Ang II, cerivastatin decreased systolic blood pressure, albuminuria, and cortical necrosis (28). These changes were associated with reduced infiltration of inflammatory cells, diminished expression of adhesion molecules, and lower levels of transcription factor (NF-{kappa}B) activity (Fig. 4Go). In rats with glomerulonephritis, simvastatin decreased mesangial cell proliferation and monocyte/macrophage infiltration (58). Statins have been shown to inhibit the proliferative actions of platelet-derived growth factor (59) and TGF-ß (56). Cytokines released during renal injury activate NF-{kappa}B and growth-regulating pathways in mesangial and tubular cells. Statins both decrease the levels of cytokines and inhibit the NF-{kappa}B-dependent gene activation, such as MCP-1 and IL-6. In humans, statins also decrease urinary albumin excretion in patients with nephrotic syndrome and in patients with type II diabetes (4). Thus, statins modulate glomerular mesangial and interstitial inflammatory process independent of lipid reduction. Clinical relevance of these observations is yet to be determined by the ongoing interventional studies.

Statins and glucose metabolism

A retrospective analysis of the WOSCOPS examining the development of new diabetes mellitus revealed that pravastatin therapy reduced the risk of developing diabetes by 30%. This prevention in the onset of diabetes was associated with significant reduction in triglyceride levels, but upon further analyses the reduction in triglycerides did not account for the effect of statins on the development of diabetes (5). Recent advances in understanding the cellular actions of statins may explain mechanisms that mediate the statin effect on insulin sensitivity. Statins may affect substrate delivery to insulin-sensitive tissues or modulate insulin-activated signaling cascades that mediate glucose uptake. Insulin increases skeletal muscle perfusion and substrate delivery by enhancing eNOS activity. As described previously, statins also increase eNOS expression, which may result in increased capillary recruitment and glucose disposal (60). Insulin activates a series of kinase cascades that involve PI3K and Akt, resulting in the translocation of glucose transporters to cell membrane and enhanced glucose uptake (60). This cascade is inhibited by circulating cytokines (TNF-{alpha} and IL-6) (60). Statins, like insulin, activate PI3K and Akt, which may play a role in glucose uptake. Statins, in addition to decreasing cytokine levels, also inhibit the cellular cascades such as Rho-kinase that inactivate the insulin receptor and signaling (20). NO is a potential intermediary, because it has been shown to stimulate skeletal muscle glucose uptake (61). Further studies (in vivo and in vitro) are needed to better understand the favorable effect of statin on glucose metabolism and insulin sensitivity.

continued...

Statins and bone remodeling

Effects of statins on bone remodeling were suggested by the finding that nitrogen-containing bisphosphonates exert their cytotoxic effects on osteoclasts by interfering with the mevalonate pathway, a step further downstream from the site of action of statins (62) (Fig. 2Go). Murine osteoclast formation in cultures was inhibited by both lovastatin and alendronate (a nitrogen-containing bisphosphonate). Furthermore, rabbit osteoclast formation and activity are also inhibited by lovastatin and by alendronate and reversed by mevalonate and geranylgeraniol, respectively (63). These findings suggest that statins, via their effects on osteoclasts, possibly inhibit bone resorption.

Statins were also shown to stimulate bone formation in several studies. In vitro, statins increase the number of osteoblasts and the amount of new bone formation in mouse skull bones (63). Similar effects were also seen in vivo when simvastatin or lovastatin was injected sc over the skull bone of mice. Furthermore, oral administration of simvastatin to rats increased trabecular bone volume and the rate of new bone formation (64). These findings were confirmed by further studies; for example, transdermal lovastatin (65) and cerivastatin were shown to increase bone mass in rodents at doses similar to the dose used in humans in the treatment of hypercholesterolemia (66). All of these findings illustrate positive effects of statins on bone remodeling in the form of inhibition of bone resorption and stimulation of bone formation. The question remains whether statins would emerge as a treatment for osteoporosis that could increase bone formation and reduce fractures. Several published studies, mostly observational, have evaluated the association of statin use and fracture risk (67, 68, 69, 70, 71); one reanalyzed data from a randomized controlled study (the LIPID trial) (72). These studies showed inconsistent results; for example, upon analysis of the General Practice Research Database, Meier et al. (6) reported a risk of hip fracture to be reduced almost by half among statin users (relative risk, 0.55; 95% confidence interval, 0.44–0.66). However, reanalysis of the General Practice Research Database using age- and gender-matched controls for each of the 218,062 patients with fractures showed no relationship between statin use and nonspine fractures (67). The adjusted relative risk for hip fracture among older women in this group was 0.80. This uncertainty regarding the effects of statins on fracture risk needs to be addressed in randomized controlled trials in the future. However, the exciting possibility of a newer generation of statin with a stronger affinity to bone, which could lower both CVD and fracture risks, remains to be seen.

Conclusion

In summary, accumulating evidence from basic research and clinical trials indicates that statins have pleiotropic effects that may largely account for the clinical benefits observed. These agents have been shown to stabilize unstable plaques, improve vascular relaxation, and promote new vessel formation. Statins reduce glomerular injury, renal disease progression, insulin resistance, and bone resorption. These actions are mediated, in part, by the effects on small G-proteins, modulation of signaling cascades, transcription, and gene expression. The clinical relevance of these effects is beginning to be recognized, and ongoing studies will be able to answer these many questions in the near future.