Background:

White matter (WM) is preferentially affected in cerebral small vessel disease (cSVD), likely due to chronic hypoperfusion. Although cilostazol (CIL) and isosorbide mononitrate (ISMN) improve outcomes in LACI trials, their acute cerebrovascular actions remain unclear. We examined whether combined CIL and ISMN cause region- and age-dependent acute changes in microvascular haemodynamics.

 

Methods:

Male and female wild-type C57BL/6J mice underwent cranial window implantation at approximately 12 weeks of age over either WM or cortical grey matter (GM). For WM windows, approximately 800 µm of cortex was aspirated to expose the corpus callosum and fitted with a custom 3D-printed window. GM windows were implanted over visual cortex without aspiration, preserving pial vasculature. Initial recordings were obtained at 4 months of age, with the same WM cohort reassessed following 8 months of ageing (1 year old).
Using a blinded crossover design, animals received vehicle or combined CIL+ISMN with a minimum 6-day washout. Haemodynamic recordings were acquired at baseline, 30 min, 1 h, 2 h, 4 h, 6 h, and 24 h using combined laser Doppler flowmetry and haemoglobin spectroscopy. Outcomes included red blood cell (RBC) flux, RBC speed, moving RBC concentration, oxygen saturation (sO₂), total haemoglobin (HbT), and derived cerebral metabolic rate of oxygen (CMRO₂). Measurements were performed in awake, head-fixed mice during resting periods. Linear mixed-effects models included drug and timepoint as fixed effects and animal ID as a random effect, with Dunnett post-hoc comparisons. Drug doses were scaled from the LACI-2 trial using body-surface-area conversion.

 

Results:

In deep tissue containing WM from young mice (n = 8), CIL+ISMN significantly decreased RBC flux (treatment effect p = 0.022; timepoint × treatment p = 0.032), with the strongest reduction observed at 6 h (estimate −0.22 ± 0.06, p = 0.0003). Moving RBC concentration was similarly reduced (p = 0.0072), while RBC speed was unaffected. CMRO₂ was significantly lowered (p = 0.016), most notably at 6 h (p = 0.0007), without accompanying changes in sO₂.
When the same mice were examined longitudinally after 8 months of ageing (n = 4), WM responses to CIL+ISMN were maintained, with significant reductions in RBC flux (p = 0.013), RBC concentration (p = 0.041), and CMRO₂ (p = 0.007).
In contrast, GM (n = 4) exhibited a significant increase in moving RBC concentration (p = 0.003), a modest decrease in HbT (p = 0.044), and a trend toward elevated sO₂ (p = 0.082), with no detectable changes in RBC flux or speed. Under sedation, arterial blood pressure did not differ between baseline, vehicle, or drug conditions.

 

Conclusions:

These findings demonstrate region-specific microvascular effects of cilostazol and isosorbide mononitrate, characterised by preserved cortical grey matter microcirculation alongside reduced red blood cell delivery and oxygen utilisation in deep tissue containing white matter. The data support an acute redistribution of microvascular resources rather than a uniform haemodynamic response. Ongoing two-photon imaging and chronic hypoperfusion studies will identify the vascular substrates and disease relevance of this redistribution under sustained treatment.