Doxorubicin is a risk factor for secondary lymphedema in cancer patients exposed to surgery or radiation. The risk is presumed to relate to its cytotoxicity. However, the present study provides initial evidence that doxorubicin directly inhibits lymph flow and this action appears distinct from its cytotoxic activity. We used real-time edge detection to track diameter changes in isolated rat mesenteric lymph vessels. Doxorubicin (0.5-20 mmol/l) progressively constricted lymph vessels and inhibited rhythmic contractions, reducing flow to 24.2% 6 7.7% of baseline. The inhibition of rhythmic contractions by doxorubicin paralleled a tonic rise in cytosolic Ca 21 concentration in lymphatic muscle cells, which was prevented by pharmacological antagonism of ryanodine receptors. Washout of doxorubicin partially restored lymph vessel contractions, implying a pharmacological effect. Subsequently, high-speed optical imaging was used to assess the effect of doxorubicin on rat mesenteric lymph flow in vivo. Superfusion of doxorubicin (0.05-10 mmol/l) maximally reduced volumetric lymph flow to 34% 6 11.6% of baseline. Likewise, doxorubicin (10 mg/kg) administered intravenously to establish clinically achievable plasma concentrations also maximally reduced volumetric lymph flow to 40.3% 6 6.0% of initial values. Our findings reveal that doxorubicin at plasma concentrations achieved during chemotherapy opens ryanodine receptors to induce "calcium leak" from the sarcoplasmic reticulum in lymphatic muscle cells and reduces lymph flow, an event linked to lymph vessel damage and the development of lymphedema. These results infer that pharmacological block of ryanodine receptors in lymphatic smooth muscle cells may mitigate secondary lymphedema in cancer patients subjected to doxorubicin chemotherapy. SIGNIFICANCE STATEMENT Doxorubicin directly inhibits the rhythmic contractions of collecting lymph vessels and reduces lymph flow as a possible mechanism of secondary lymphedema, which is associated with the administration of anthracycline-based chemotherapy. The inhibitory effects of doxorubicin on rhythmic contractions and flow in isolated lymph vessels were prevented by pharmacological block of ryanodine receptors, thereby identifying the ryanodine receptor family of proteins as potential therapeutic targets for the development of new antilymphedema medications.

The lymphatic system contributes to body homeostasis by clearing fluid, lipids, plasma proteins and immune cells from the interstitial space. Many studies have been performed to understand lymphatic function under normal conditions and during disease. Nevertheless, a further improvement in quantification of lymphatic behavior is needed. Here, we present advanced bright-field microscopy for in vivo imaging of lymph vessels (LVs) and automated quantification of lymphatic function at a temporal resolution of 2 milliseconds. Full frame videos were compressed and recorded continuously at up to 540 frames per second. A new edge detection algorithm was used to monitor vessel diameter changes across multiple cross sections, while individual cells in the LVs were tracked to estimate flow velocity. The system performance initially was verified in vitro using 6- and 10-μm microspheres as cell phantoms on slides and in 90-μm diameter tubes at flow velocities up to 4 cm/second. Using an in vivo rat model, we explored the mechanisms of lymphedema after surgical lymphadenectomy of the mesentery. The system revealed reductions of mesenteric LV contraction and flow rate. Thus, the described imaging system may be applicable to the study of lymphatic behavior during therapeutic and surgical interventions, and potentially during lymphatic system diseases.

The different responses of women and men to cardiovascular drugs reflect gender -specific variances in pharmacokinetic profiles and drug sensitivities coupled to inherent differences in the underlying physiology of each sex. Thus, many common cardiovascular drugs exhibit gender -specific therapeutic and adverse effects. For example, the QT interval of the electrocardiogram is longer in women compared to men, and accordingly, drugs that prolong the QT interval are more likely to cause lethal ventricular arrhythmias in female than male patients. As more clinical drug trials include women subjects, our improved knowledge base for assessing the risk/benefit ratio for cardiovascular drugs in women will enable us to consider gender as one factor in prescribing drugs and adjusting drug loading and maintenance dosages. This short review will present evidence for gender- related differences in the responses to common cardiovascular drugs including statins, antiplatelet and antithrombotic agents, β-blockers, digoxin, vasodilator therapies, and drugs associated with the Long QT Syndrome.

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Background and Purpose: Doxorubicin (DOX) is a risk factor for arm lymphedema in breast cancer patients. We reported that DOX opens ryanodine receptors (RYRs) to enact “calcium leak,” which disrupts the rhythmic contractions of lymph vessels (LVs) to attenuate lymph flow. Here, we evaluated whether dantrolene, a clinically available RYR1 subtype antagonist, prevents the detrimental effects of DOX on lymphatic function.Experimental Approach: Isolated rat mesenteric LVs were cannulated, pressurized (4–5 mm Hg) and equilibrated in physiological salt solution and Fura-2AM. Video microscopy recorded changes in diameter and Fura-2AM fluorescence tracked cytosolic free calcium ([Ca2+i]). High-speed in vivo microscopy assessed mesenteric lymph flow in anesthetized rats. Flow cytometry evaluated RYR1 expression in freshly isolated mesenteric lymphatic muscle cells (LMCs).Key Results: DOX (10 μmol/L) increased resting [Ca2+i] by 17.5 ± 3.7% in isolated LVs (n = 11). The rise in [Ca2+i] was prevented by dantrolene (3 μmol/L; n = 10). A single rapid infusion of DOX (10 mg/kg i.v.) reduced positive volumetric lymph flow to 29.7 ± 10.8% (n = 7) of baseline in mesenteric LVs in vivo. In contrast, flow in LVs superfused with dantrolene (10 μmol/L) only decreased to 76.3 ± 14.0% (n = 7) of baseline in response to DOX infusion. Subsequently, expression of the RYR1 subtype protein as the presumed dantrolene binding site was confirm in isolated mesenteric LMCs by flow cytometry.Conclusion and Implications: We conclude that dantrolene attenuates the acute impairment of lymph flow by DOX and suggest that its prophylactic use in patients subjected to DOX chemotherapy may lower lymphedema risk.