Causal effect of insulin resistance on small vessel stroke and Alzheimer's disease: A Mendelian randomization analysis

Triglyceride-glucose index is associated with a higher risk of stroke in a hypertensive population

BACKGROUND

This study aimed to evaluate the association of triglyceride-glucose (TyG) index, an insulin resistance surrogate biomarker, with first stroke in a hypertensive population and to explore potential influencing factors.

METHODS

This study, a cohort study among a rural Chinese hypertensive population, utilized data from the China Stroke Primary Prevention Trial (CSPPT). The TyG index was calculated as ln [fasting triglyceride (mg/dL) × fasting glucose (mg/dL)/2]. Multivariate analysis using Cox proportional hazards models was conducted.

RESULTS

A total of 7569 hypertensive patients were included in this study. When TyG index was assessed as quartiles, compared with the reference group (Quartile 1), the hazard ratio of stroke was 1.04 in Quartile 2, 1.43 in Quartile 3, and 1.45 in Quartile 4, with a significant trend test (P = 0.013). When Quartiles 3 and 4 were combined (≥ 8.8), the hazard ratio was 1.41 compared with combined Quartiles 1 and 2 (< 8.8). Similar findings were observed for the association of TyG index with ischemic stroke. Further, a joint effect of baseline TyG index and age on first stroke was found. Using the group with TyG < 8.8 and age < 60 years as a reference, the highest hazard ratio of stroke was found in the group with a higher TyG index and aged 60 or greater (HR: 2.15, 95% CI 1.50, 3.07, P < 0.001).

CONCLUSIONS

In a hypertensive population, baseline TyG index was associated with a significantly higher risk of first stroke. In addition, age was a significant effect modifier for this association.

d-Amino acids: new clinical pathways for brain diseases

Free d-amino acids (d-AAs) are emerging as a novel and important class of signaling molecules in many organs, including the brain and endocrine systems. There has been considerable progress in our understanding of the fundamental roles of these atypical messengers, with increasingly recognized implications in a wide range of neuropathologies, including schizophrenia (SCZ), epilepsy, Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), substance abuse, and chronic pain, among others. Research has enabled the discovery that d-serine, d-aspartate and more recently d-cysteine are essential for the healthy development and function of the central nervous system (CNS). We discuss recent progress that has profoundly transformed our vision of numerous physiological processes but has also shown how d-AAs are now offering therapeutic promise in clinical settings for several human diseases.

The Role of Insulin-like Growth Factor I in Mechanisms of Resilience and Vulnerability to Sporadic Alzheimer's Disease

Despite decades of intense research, disease-modifying therapeutic approaches for Alzheimer's disease (AD) are still very much needed. Apart from the extensively analyzed tau and amyloid pathological cascades, two promising avenues of research that may eventually identify new druggable targets for AD are based on a better understanding of the mechanisms of resilience and vulnerability to this condition. We argue that insulin-like growth factor I (IGF-I) activity in the brain provides a common substrate for the mechanisms of resilience and vulnerability to AD. We postulate that preserved brain IGF-I activity contributes to resilience to AD pathology as this growth factor intervenes in all the major pathological cascades considered to be involved in AD, including metabolic impairment, altered proteostasis, and inflammation, to name the three that are considered to be the most important ones. Conversely, disturbed IGF-I activity is found in many AD risk factors, such as old age, type 2 diabetes, imbalanced diet, sedentary life, sociality, stroke, stress, and low education, whereas the Apolipoprotein (Apo) E4 genotype and traumatic brain injury may also be influenced by brain IGF-I activity. Accordingly, IGF-I activity should be taken into consideration when analyzing these processes, while its preservation will predictably help prevent the progress of AD pathology. Thus, we need to define IGF-I activity in all these conditions and develop a means to preserve it. However, defining brain IGF-I activity cannot be solely based on humoral or tissue levels of this neurotrophic factor, and new functionally based assessments need to be developed.

Co-administration of dl-3-n-butylphthalide and neprilysin is neuroprotective in Alzheimer disease associated with mild traumatic brain injury

dl-3-n-Butylphthalide is a potent synthetic Chinese celery extract that is highly efficient in inducing neuroprotection in concussive head injury (CHI), Parkinson's disease, Alzheimer's disease, stroke as well as depression, dementia, anxiety and other neurological diseases. Thus, there are reasons to believe that dl-3-n-butylphthalide could effectively prevent Alzheimer's disease brain pathology. Military personnel during combat operation or veterans are often the victims of brain injury that is a major risk factor for developing Alzheimer's disease in their later lives. In our laboratory we have shown that CHI exacerbates Alzheimer's disease brain pathology and reduces the amyloid beta peptide (AβP) inactivating enzyme neprilysin. We have used TiO2 nanowired-dl-3-n-butylphthalide in attenuating Parkinson's disease brain pathology exacerbated by CHI. Nanodelivery of dl-3-n-butylphthalide appears to be more potent as compared to the conventional delivery of the compound. Thus, it would be interesting to examine the effects of nanowired dl-3-n-butylphthalide together with nanowired delivery of neprilysin in Alzheimer's disease model on brain pathology. In this investigation we found that nanowired delivery of dl-3-n-butylphthalide together with nanowired neprilysin significantly attenuated brain pathology in Alzheimer's disease model with CHI, not reported earlier. The possible mechanism and clinical significance is discussed based on the current literature.

Distinct Brain Proteomic Signatures in Cerebral Small Vessel Disease Rat Models of Hypertension and Cerebral Amyloid Angiopathy

Cerebral small vessel diseases (CSVDs) are prominent contributors to vascular cognitive impairment and dementia and can arise from a range of etiologies. Cerebral amyloid angiopathy (CAA) and hypertension (HTN), both prevalent in the elderly population, lead to cerebral microhemorrhages, macrohemorrhages, and white matter damage. However, their respective underlying mechanisms and molecular events are poorly understood. Here, we show that the transgenic rat model of CAA type 1 (rTg-DI) exhibits perivascular inflammation that is lacking in the spontaneously hypertensive stroke-prone (SHR-SP) rat model of HTN. Alternatively, SHR-SP rats display notable dilation of arteriolar perivascular spaces. Comparative proteomics analysis revealed few shared altered proteins, with key proteins such as ANXA3, H2A, and HTRA1 unique to rTg-DI rats, and Nt5e, Flot-1 and Flot-2 unique to SHR-SP rats. Immunolabeling confirmed that upregulation of ANXA3, HTRA1, and neutrophil extracellular trap proteins were distinctly associated with rTg-DI rats. Pathway analysis predicted activation of TGF-β1 and TNFα in rTg-DI rat brain, while insulin signaling was reduced in the SHR-SP rat brain. Thus, we report divergent protein signatures associated with distinct cerebral vessel pathologies in the SHR-SP and rTg-DI rat models and provide new mechanistic insight into these different forms of CSVD.

Mendelian randomization highlights significant difference and genetic heterogeneity in clinically diagnosed Alzheimer's disease GWAS and self-report proxy phenotype GWAX

BACKGROUND

Until now, Mendelian randomization (MR) studies have investigated the causal association of risk factors with Alzheimer's disease (AD) using large-scale AD genome-wide association studies (GWAS), GWAS by proxy (GWAX), and meta-analyses of GWAS and GWAX (GWAS+GWAX) datasets. However, it currently remains unclear about the consistency of MR estimates across these GWAS, GWAX, and GWAS+GWAX datasets.

METHODS

Here, we first selected 162 independent educational attainment genetic variants as the potential instrumental variables (N = 405,072). We then selected one AD GWAS dataset (N = 63,926), two AD GWAX datasets (N = 314,278 and 408,942), and three GWAS+GWAX datasets (N = 388,324, 455,258, and 472,868). Finally, we conducted a MR analysis to evaluate the impact of educational attainment on AD risk across these datasets. Meanwhile, we tested the genetic heterogeneity of educational attainment genetic variants across these datasets.

RESULTS

In AD GWAS dataset, MR analysis showed that each SD increase in years of schooling (about 3.6 years) was significantly associated with 29% reduced AD risk (OR=0.71, 95% CI: 0.60-0.84, and P=1.02E-04). In AD GWAX dataset, MR analysis highlighted that each SD increase in years of schooling significantly increased 84% AD risk (OR=1.84, 95% CI: 1.59-2.13, and P=4.66E-16). Meanwhile, MR analysis suggested the ambiguous findings in AD GWAS+GWAX datasets. Heterogeneity test indicated evidence of genetic heterogeneity in AD GWAS and GWAX datasets.

CONCLUSIONS

We highlighted significant difference and genetic heterogeneity in clinically diagnosed AD GWAS and self-report proxy phenotype GWAX. Our MR findings are consistent with recent findings in AD genetic variants. Hence, the GWAX and GWAS+GWAX findings and MR findings from GWAX and GWAS+GWAX should be carefully interpreted and warrant further investigation using the AD GWAS dataset.