Spatio-temporal clustering analysis using generalized lasso with an application to reveal the spread of Covid-19 cases in Japan

This study addressed the issue of determining multiple potential clusters with regularization approaches for the purpose of spatio-temporal clustering. The generalized lasso framework has flexibility to incorporate adjacencies between objects in the penalty matrix and to detect multiple clusters. A generalized lasso model with two L 1 penalties is proposed, which can be separated into two generalized lasso models: trend filtering of temporal effect and fused lasso of spatial effect for each time point. To select the tuning parameters, the approximate leave-one-out cross-validation (ALOCV) and generalized cross-validation (GCV) are considered. A simulation study is conducted to evaluate the proposed method compared to other approaches in different problems and structures of multiple clusters. The generalized lasso with ALOCV and GCV provided smaller MSE in estimating the temporal and spatial effect compared to unpenalized method, ridge, lasso, and generalized ridge. In temporal effects detection, the generalized lasso with ALOCV and GCV provided relatively smaller and more stable MSE than other methods, for different structure of true risk values. In spatial effects detection, the generalized lasso with ALOCV provided higher index of edges detection accuracy. The simulation also suggested using a common tuning parameter over all time points in spatial clustering. Finally, the proposed method was applied to the weekly Covid-19 data in Japan form March 21, 2020, to September 11, 2021, along with the interpretation of dynamic behavior of multiple clusters.

Metformin confers longitudinal cardiac protection by preserving mitochondrial homeostasis following myocardial ischemia/reperfusion injury

PURPOSE

Myocardial ischemia-reperfusion (I/R) injury is associated with systemic oxidative stress, cardiac mitochondrial homeostasis, and cardiomyocyte apoptosis. Metformin has been recognized to attenuate cardiomyocyte apoptosis. However, the longitudinal effects and pathomechanism of metformin on the regulation of myocardial mitohormesis following I/R treatment remain unclear. This study aimed to investigate the longitudinal effects and mechanism of metformin in regulating cardiac mitochondrial homeostasis by serial imaging with the 18-kDa translocator protein (TSPO)-targeted positron emission tomography (PET) tracer ¹⁸F-FDPA.

METHODS

Myocardial I/R injury was established in Sprague-Dawley rats, which were treated with or without metformin (150 mg/kg per day). Serial gated ¹⁸F-FDG and ¹⁸F-FDPA PET imaging were performed at 1, 4, and 8 weeks after surgery, followed by analysis of ventricular remodelling and cardiac mitochondrial homeostasis. The correlation between Hsp60 and ¹⁸F-FDPA uptake was analyzed. After PET imaging, the activity of antioxidant enzymes, immunostaining, and western blot analysis were performed to analyze the spatio-temporal effects and pathomechanism of metformin for cardiac protection after myocardial I/R injury.

RESULTS

Oxidative stress and apoptosis increased 1 week after myocardial I/R injury (before significant progression of ventricular remodelling). TSPO expression was correlated with Hsp60 expression and was co-localized with inflammatory CD68⁺ macrophages in the infarct area, and TSPO uptake was associated with an upregulation of AMPK-p/AMPK and a downregulation of Bcl-2/Bax. However, these effects were reversed with metformin treatment. Eight weeks after myocardial I/R injury (representing the advanced stage of heart failure), ¹⁸F-FDPA uptake in myocardial cells in the distal non-infarct area increased without CD68⁺ expression, whereas the activity decreased with metformin treatment.

CONCLUSION

Taken together, these results show that a prolonged metformin treatment has pleiotropic protective effects against myocardial I/R injury associated with a regional and temporal dynamic balance between mitochondrial homeostasis and cardiac outcome, which were assessed by TSPO-targeted imaging during cardiac remodelling.