. Statins, incident Alzheimer disease, change in cognitive function, and neuropathology. Neurology. 2008 May 6;70(19 Pt 2):1795-802. PubMed.

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  1. Statins have been shown to be beneficial in preventing many different diseases in addition to cardiovascular disease, from osteoporosis to prostate cancer. Whether statins might be beneficial for those at risk of Alzheimer disease or suffering from the disease remains unclear. The most recent manuscript on this subject is a study by David Bennett’s group, examining cases from the Nun Study. Arvanitakis et al. have examined 929 cases from the Nun Study to investigate whether statins modify the pathology associated with AD. The group finds a striking absence of any effect in every measure examined. The group examined whether statin use was associated with any differences in incident Alzheimer cases but failed to observe any effect. They also examined whether statin use was associated with any change in plaque or tangle production, but also failed to observe any effect. The absence of any effects is an important finding, but is difficult to interpret because it comes on the heels of other studies, some of which are positive, others that are negative.

    One of the key considerations in evaluating a study such as this is numbers. Large numbers of cases are needed to examine the effects of medications on disease parameters because typically only a small fraction of patients are taking any particular medication and only a fraction of those exhibit the specific phenotype of interest. In the current study, the group started with 929 cases, with 119 cases positive for statin use. The use of lipid-lowering medication is presumably by self-report, and there is no description of duration of medication utilization, whether the medication was taken continuously or dosing. The group first used these cases to examine incident AD. Next, the group went on to examine effects on pathology. Only 199 or 231 out of the 989 cases had amyloid or tangle pathology, respectively; 16.6 percent of these cases used statins, which corresponds to 33 or 38 cases for amyloid or tangle pathology. Presumably, only about one-third of these cases, approximately 10-12 cases, used a brain penetrant statin, such as simvastatin. Obtaining statistical significance with such small numbers of cases is difficult.

    Regardless of the considerations of number or power, I am struck by the absence of any effect associated with the statins. There was no overall effect for virtually any measure. The group did stratify the results by type of medication—lipophilic statin, lipophobic statin or non-statin agent—as well as by ApoE genotype. These stratifications could be important because other groups have observed more significant effects in ApoE4 subjects (Kivipelto et al., 2005; Rovio et al., 2005). In addition, our results suggest that the potent brain penetrant statin, simvastatin, is more effective than lovastatin, which is brain penetrant but less potent and also more effective than atorvastatin, which is not brain penetrant (Wolozin et al., 2007). Stratification by lipophilicity did not produce a statistically significant effect in most outcomes, but the data suffer from very large confidence interval, suggesting that statistical power was a significant issue. The problem is that the numbers get very small very quickly, which could easily lead to a false negative result. One measure, amyloid load, did show a weakly significant effect for users of lipophilic statins (simvastatin and lovastatin).

    The lack of any effect is striking and contrasts with a recent study from the Cache County cohort in which Li et al. observed that subjects taking statins showed a significant reduction in neurofibrillary plaque formation, but no change in neuritic plaque formation (Li et al., 2007). In a smaller study published previously, we examined plaque pathology and markers of inflammation. We observed no change in plaque pathology, but a striking decrease in inflammation (Wolozin et al., 2006). Both of these studies parallel observations by Ling Li in the APP transgenic mouse model showing that simvastatin is associated with improved memory function that is not correlated with changes in amyloid load (Li et al., 2006). It is unfortunate that Bennett’s group did not examine inflammatory markers, which are known to decrease in subjects taking statins. Two prospective trials have been done specifically focused on the issue of statins and AD. The trial by Simons used simvastatin (Simons et al., 2002), and a more recent trial by Sparks used atorvastatin (Sparks et al., 2005). Both showed some benefit to patients with AD, but both suffered from low power and benefits were observable mainly after post-hoc analysis of subgroups. Interestingly, both prospective studies suggest that there might be some effect on amyloid levels, which contrasts with the studies of pathology in animals and humans. One other study of relevance is that by Hinerfeld et al., which observed reduced CSF amyloid in subjects with PS1 mutations taking simvastatin, but not in sporadic AD cases and not with other statins (Hinerfeld et al., 2007).

    The discrepancy between the work by Arvanitakis et al. and the previously published manuscripts is difficult to reconcile. It could be that in studies of pharmaco-epidemiology, medication-use history and large numbers are both as important as accurate diagnostic criteria for evaluating data. Without these factors, studies might be prone to discrepant results. As the data accumulate, a meta-analysis might be informative.

    References:

    . Statins differentially affect amyloid precursor protein metabolism in presymptomatic PS1 and non-PS1 subjects. Arch Neurol. 2007 Nov;64(11):1672-3. PubMed.

    . Obesity and vascular risk factors at midlife and the risk of dementia and Alzheimer disease. Arch Neurol. 2005 Oct;62(10):1556-60. PubMed.

    . Statin therapy is associated with reduced neuropathologic changes of Alzheimer disease. Neurology. 2007 Aug 28;69(9):878-85. PubMed.

    . Simvastatin enhances learning and memory independent of amyloid load in mice. Ann Neurol. 2006 Dec;60(6):729-39. PubMed.

    . Leisure-time physical activity at midlife and the risk of dementia and Alzheimer's disease. Lancet Neurol. 2005 Nov;4(11):705-11. PubMed.

    . Treatment with simvastatin in normocholesterolemic patients with Alzheimer's disease: A 26-week randomized, placebo-controlled, double-blind trial. Ann Neurol. 2002 Sep;52(3):346-50. PubMed.

    . Atorvastatin for the treatment of mild to moderate Alzheimer disease: preliminary results. Arch Neurol. 2005 May;62(5):753-7. PubMed.

    . Simvastatin is associated with a reduced incidence of dementia and Parkinson's disease. BMC Med. 2007;5:20. PubMed.

    . Re-assessing the relationship between cholesterol, statins and Alzheimer's disease. Acta Neurol Scand Suppl. 2006;185:63-70. PubMed.

  2. The recent study by Arvanitakis et al. shows no effect of statins on incident AD, cognitive decline, and related neuropathology in a group of elderly Catholic clergy. But their data may support a different conclusion. Presumably, participants treated with statins were at elevated cardiovascular risk compared to those not treated. In fact, the authors caution that a weakness of the study is derived from “the likely possibility of indication bias (statin exposure is non-random).” Numerous studies have demonstrated a positive correlation between increased cardiovascular risk and AD. Based on this, one might expect the statin-treated group in the present study to show accelerated cognitive decline and increased AD, but they did not. Does this mean a lack of effect of statins or a positive effect (i.e., normalization of dementia risk in a high cardiovascular risk population)?

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