Posterior reversible encephalopathy syndrome in stroke-prone spontaneously hypertensive rats on high-salt diet

Effect of high-fat diet on cerebral pathological changes of cerebral small vessel disease in SHR/SP rats

Cerebral small vessel diseases (CSVD) are neurological disorders associated with microvessels, manifested pathologically as white matter (WM) changes and cortical microbleeds, with hypertension as a risk factor. Additionally, a high-fat diet (HFD) can affect peripheral vessel health. Our study explored how HFD affects cerebral small vessels in normotensive WKY, hypertensive SHR, and SHR/SP rats. The MRI results revealed that HFD specifically increased WM hyperintensity in SHR/SP rats. Pathologically, it increased WM pallor and vacuolation in SHR and SHR/SP rats. Levels of blood-brain barrier (BBB) protein claudin 5 were decreased in SHR and SHR/SP compared to WKY, with HFD having minimal impact on these levels. Conversely, collagen IV levels remained consistent among the rat strains, which were increased by HFD. Consequently, HFD caused vessel leakage in all rat strains, particularly within the corpus callosum of SHR/SP rats. To understand the underlying mechanisms, we assessed the levels of hypoxia-inducible factor-1α (HIF-1α), Gp91-phox, and neuroinflammatory markers astrocytes, and microglia were increased in SHR and SHR/SP compared to WKY and were further elevated by HFD in all rat strains. Gp91-phox was also increased in SHR and SHR/SP compared to WKY, with HFD causing an increase in WKY but little effect in SHR and SHR/SP. In conclusion, our study demonstrates that HFD, in combined with hypertension, intensifies cerebral pathological alterations in CSVD rats. This exacerbation involves increased oxidative stress and HIF-1α in cerebral vessels, triggering neuroinflammation, vascular basement membrane remodeling, IgG leakage, and ultimately WM damage.

Experimental Models of Posterior Reversible Encephalopathy Syndrome: A Review From Pathophysiology to Therapeutic Targets

Posterior reversible encephalopathy syndrome (PRES) is a clinical and radiological entity characterized by nonspecific symptomatology (eg, headache, visual disturbances, encephalopathy, and seizures) and classically cortical and subcortical vasogenic edema predominantly affecting the parietooccipital region. PRES etiologies are usually dichotomized into toxic PRES (eg, antineoplastic drugs, illicit drugs) and clinical condition-associated PRES (eg, acute hypertension, dysimmune disorders). Although the pathophysiology of PRES remains elusive, 2 main pathogenic hypotheses have been suggested: cerebral hyperperfusion due to acute hypertension and cerebral hypoperfusion related to endothelial dysfunction. Research into the pathogenesis of PRES has emerged through the development of animal models in the last decade. The motivation for developing a suitable PRES model is 2-fold: to fill in knowledge gaps of the pathophysiological mechanisms involved, and to open new perspectives for clinical assessment of pharmacological targets to improve therapeutic management of PRES. All current models of PRES have a hypertensive background, on which other triggers (acute hypertension, inflammatory, drug toxicity) have been added to address specific facets of PRES (eg, seizures). The initial model consisted in inducing a reduced uterine perfusion pressure that mimics preeclampsia, a leading cause of PRES. More recently, a model of stroke-prone spontaneously hypertensive rats on high-salt diet, originally developed for hypertensive small vessel disease and vascular cognitive impairment, has been studied in PRES. This review aims to discuss, depending on the research objective, the benefits and limitations of current experimental approaches and thus to define the desirable characteristics for studying the pathophysiology of PRES and developing new therapies.

Characterizing the Neuroimaging and Histopathological Correlates of Cerebral Small Vessel Disease in Spontaneously Hypertensive Stroke-Prone Rats

Introduction: Spontaneously hypertensive stroke-prone rats (SHRSP) are used to model clinically relevant aspects of human cerebral small vessel disease (CSVD). To decipher and understand the underlying disease dynamics, assessment of the temporal progression of CSVD histopathological and neuroimaging correlates is essential. Materials and Methods: Eighty age-matched male SHRSP and control Wistar Kyoto rats (WKY) were randomly divided into four groups that were aged until 7, 16, 24 and 32 weeks. Sensorimotor testing was performed weekly. Brain MRI was acquired at each study time point followed by histological analyses of the brain. Results: Compared to WKY controls, the SHRSP showed significantly higher prevalence of small subcortical hyperintensities on T2w imaging that progressed in size and frequency with aging. Volumetric analysis revealed smaller intracranial and white matter volumes on brain MRI in SHRSP compared to age-matched WKY. Diffusion tensor imaging (DTI) showed significantly higher mean diffusivity in the corpus callosum and external capsule in WKY compared to SHRSP. The SHRSP displayed signs of motor restlessness compared to WKY represented by hyperactivity in sensorimotor testing at the beginning of the experiment which decreased with age. Distinct pathological hallmarks of CSVD, such as enlarged perivascular spaces, microbleeds/red blood cell extravasation, hemosiderin deposits, and lipohyalinosis/vascular wall thickening progressively accumulated with age in SHRSP. Conclusions: Four stages of CSVD severity in SHRSP are described at the study time points. In addition, we find that quantitative analyses of brain MRI enable identification of in vivo markers of CSVD that can serve as endpoints for interventional testing in therapeutic studies.

Whey Protein and Its Components Lactalbumin and Lactoferrin Affect Energy Balance and Protect against Stroke Onset and Renal Damage in Salt-Loaded, High-Fat Fed Male Spontaneously Hypertensive Stroke-Prone Rats

BACKGROUND

Whey protein (WH)-enriched diets are reported to aid in weight loss and to improve cardiovascular health. However, the bioactive components in whey responsible for causing such effects remain unidentified.

OBJECTIVE

We determined the effects of whey and its components [α-lactalbumin (LA) and lactoferrin (LF)] on energy balance, glucose tolerance, gut hormones, renal damage, and stroke onset in rats.

METHODS

Male spontaneously hypertensive stroke-prone (SHRSP) rats (age 8 wk) were fed isocaloric high-fat (40% kcal) and high-salt (4% wt/wt) diets (n = 8-10/group) and randomized for 8 wk to diets enriched as follows: control (CO): 15% kcal from egg albumin, 45% kcal from carbohydrate; WH: 20%kcal WH isolate + 15% kcal egg albumin; LA: 20% kcal LA  + 15% kcal egg albumin; or LF: 20% kcal lactoferrin + 15% kcal egg albumin. Measurements included energy balance (food intake, energy expenditure, and body composition), stroke-related behaviors, brain imaging, glucose tolerance, metabolic hormones, and tissue markers of renal damage. Data were analyzed by linear mixed models with repeated measures or 1-way ANOVA.

RESULTS

Diets enriched with WH, LA, or LF increased survival, with 25% of rats fed these diets exhibiting stroke-associated morbidity, whereas 90% of CO rats were morbid by 8 wk (P < 0.05). The nephritis scores of rats fed WH-, LA-, or LF-enriched diets were 80%, 92%, and 122% lower than those of COs (P = 0.001). The mRNA abundances of renin and osteopontin were 100-600% lower in rats fed WH-, LA-, or LF-enriched diets than in COs (P < 0.05). Urine albumin concentrations and albumin-to-creatinine ratios were 200% lower in rats fed LF-enriched diets than in COs (P < 0.05). Compared with COs, rats fed LF-enriched diets for 2-3 wk had food intake decreased by 29%, body weight decreased by 13-19%, lean mass decreased by 12-19%, and fat mass decreased by 20% (P < 0.001). Relative to COs, rats fed WH and LA had food intake decreased by 10% (P < 0.1), but COs had 12-45% lower weight than rats fed LA- and WH-enriched diets by 3 wk (P < 0.01). Compared with COs, rats fed WH-enriched diets increased energy expenditure by 7%, whereas, rats fed LA-enriched diets had energy expenditure acutely decreased by 7% during the first 4 d, and rats fed LF-enriched diets had energy expenditure decreased by 7-17% throughout the first week ( P < 0.001). Rats fed LA- and LF-enriched diets had blood glucose decreased by 14-19% (P < 0.05) and WH by 9% (P = 0.1), relative to COs. Compared with COs, rats fed LF had GIP decreased by 90% and PYY by 87% (P < 0.05).

CONCLUSION

Together, these findings indicate that whey and its components α-lactalbumin and lactoferrin improved energy balance and glycemic control, and protected against the onset of neurological deficits associated with stroke and renal damage in male SHRSP rats.

Neuropathic pain releasing calcitonin gene related peptide protects against stroke in rats

Neuropathic pain (NPP) is deemed as a potential risk of stroke; however, recent pieces of evidence showed that calcitonin gene-related peptide is involving in pain progression as well as organ protection. The mechanisms underlying the neuroprotection of calcitonin gene-related peptide are yet poorly described with respect to stroke. The present study showed that the elevated level of calcitonin gene-related peptide-induced by NPP exerts a protective effect against stroke in rats, which was further confirmed in vivo and vitro via mitigation of inflammatory response, inhibition of neuronal cell apoptosis, and increase in regional cerebral blood flow. Repetitive transcranial magnetic stimulation at trigeminal ganglion was performed to simulate to facilitate the release of calcitonin gene-related peptide for a similar neuroprotective effect. Together, these findings posit that the release of calcitonin gene-related peptide-induced by NPP or repetitive transcranial magnetic stimulation protects against stroke in rats. Thus, repetitive transcranial magnetic stimulation could have high application prospects for the prevention and treatment of stroke.

Blood-Brain Barrier Disruption as a Potential Target for Therapy in Posterior Reversible Encephalopathy Syndrome: Evidence From Multimodal MRI in Rats

Background: To explore blood-brain barrier disruption in hypertensive posterior reversible encephalopathy syndrome. Methods: The hypertension rat models were successfully established and scanned on 7T micro-MRI. MRI parameter maps including apparent diffusion coefficient, T1 value, and perfusion metrics such as cerebral blood volume, cerebral blood flow, mean transit time and time to peak maps, were calculated. Results: The ADC values of the experimental group were higher than those of the control group both in cortical (P < 0.01) and subcortical (P < 0.05) regions. Voxel-wise analysis of ADC maps localized vasogenic edema primarily to the posterior portion of the brain. The increase in cerebral blood volume and cerebral blood flow values were found in the cortical and subcortical regions of rats with acute hypertension. No correlation was found between perfusion metrics and mean arterial pressure. The Evans blue dye content was higher in the posterior brain region than the anterior one (P < 0.05). Conclusions: Cerebral vasogenic edema resulting from acute hypertension supports the hypothesis of posterior reversible encephalopathy syndrome as the result of blood-brain barrier disruption, which maybe the potential therapeutic target for intervention.

Pathophysiology of Lacunar Stroke: History's Mysteries and Modern Interpretations

Since the term "lacune" was adopted in the 1800s to describe infarctions from cerebral small vessels, their underlying pathophysiological basis remained obscure until the 1960s when Charles Miller Fisher performed several autopsy studies of stroke patients. He observed that the vessels displayed segmental arteriolar disorganization that was associated with vessel enlargement, hemorrhage, and fibrinoid deposition. He coined the term "lipohyalinosis" to describe the microvascular mechanism that engenders small subcortical infarcts in the absence of a compelling embolic source. Since Fisher's early descriptions of lipohyalinosis and lacunar stroke (LS), there have been many advancements in the understanding of this disease process. Herein, we review lipohyalinosis as it relates to modern concepts of cerebral small vessel disease (cSVD). We discuss clinical classifications of LS as well as radiographic definitions based on modern neuroimaging techniques. We provide a broad and comprehensive overview of LS pathophysiology both at the vessel and parenchymal levels. We also comment on the role of biomarkers, the possibility of systemic disease processes, and advancements in the genetics of cSVD. Lastly, we assess preclinical models that can aid in studying LS disease pathogenesis. Enhanced understanding of this highly prevalent disease will allow for the identification of novel therapeutic targets capable of mitigating disease sequelae.