The Vasodilator Effect of a Cream Containing 10% Menthol and 15% Methyl Salicylate on Random-Pattern Skin Flaps in Rats

Short-term cutaneous vasodilatory and thermosensory effects of topical methyl salicylate

Introduction

Methyl salicylate, the main compound of wintergreen oil, is widely used in topical applications. However, its vascular and thermosensory effects are not fully understood. The primary aim was to investigate the effects of topical methyl salicylate on skin temperature (Tskin), skin microcirculation (MCskin) and muscle oxygen saturation (SmO2) compared to a placebo gel. The secondary aim was to assess thermosensory responses (thermal sensation, thermal comfort) and to explore to which extent these sensations correspond to the physiological responses over time.

Methods

21 healthy women (22.2 ± 2.9 years) participated in this single-blind, randomized controlled trial. Custom-made natural wintergreen oil (12.9%), containing methyl salicylate (>99%) and a placebo gel, 1 g each, were applied simultaneously to two paravertebral skin areas (5 cm × 10 cm, Th4-Th7). Tskin (infrared thermal imaging), MCskin (laser speckle contrast imaging) and SmO2 (deep tissue oxygenation monitoring) and thermosensation (Likert scales) were assessed at baseline (BL) and at 5-min intervals during a 45 min post-application period (T0-T45).

Results

Both gels caused an initial decrease in Tskin, with Tskin(min) at T5 for both methyl salicylate (BL-T5: Δ-3.36°C) and placebo (BL-T5: Δ-3.90°C), followed by a gradual increase (p < .001). Methyl salicylate gel resulted in significantly higher Tskin than placebo between T5 and T40 (p < .05). For methyl salicylate, MCskin increased, with MCskin(max) at T5 (BL-T5: Δ88.7%). For placebo, MCskin decreased (BL-T5: Δ-17.5%), with significantly lower values compared to methyl salicylate between T0 and T45 (p < .05). Both gels had minimal effects on SmO2, with no significant differences between methyl salicylate and placebo (p > .05). Thermal sensation responses to topical methyl salicylate ranged from "cool" to "hot", with more intense sensations reported at T5.

Discussion

The findings indicate that topical methyl salicylate induces short-term cutaneous vasodilation, but it may not enhance skeletal muscle blood flow. This study highlights the complex sensory responses to its application, which may be based on the short-term modulation of thermosensitive transient receptor potential channels.

Standardized Pre-clinical Surgical Animal Model Protocol to Investigate the Cellular and Molecular Mechanisms of Ischemic Flap Healing

BACKGROUND

Some of the most complex surgical interventions to treat trauma and cancer include the use of locoregional pedicled and free autologous tissue transfer flaps. While the techniques used for these reconstructive surgery procedures have improved over time, flap complications and even failure remain a significant clinical challenge. Animal models are useful in studying the pathophysiology of ischemic flaps, but when repeatability is a primary focus of a study, conventional in-vivo designs, where one randomized subset of animals serves as a treatment group while a second subset serves as a control, are at a disadvantage instigated by greater subject-to-subject variability. Our goal was to provide a step-by-step methodological protocol for creating an alternative standardized, more economical, and transferable pre-clinical animal research model of excisional full-thickness wound healing following a simulated autologous tissue transfer which includes the primary ischemia, reperfusion, and secondary ischemia events with the latter mimicking flap salvage procedure.

RESULTS

Unlike in the most frequently used classical unilateral McFarlane's caudally based dorsal random pattern skin flap model, in the herein described bilateral epigastric fasciocutaneous advancement flap (BEFAF) model, one flap heals under normal and a contralateral flap-under perturbed conditions or both flaps heal under conditions that vary by one within-subjects factor. We discuss the advantages and limitations of the proposed experimental approach and, as a part of model validation, provide the examples of its use in laboratory rat (Rattus norvegicus) axial pattern flap healing studies.

CONCLUSIONS

This technically challenging but feasible reconstructive surgery model eliminates inter-subject variability, while concomitantly minimizing the number of animals needed to achieve adequate statistical power. BEFAFs may be used to investigate the spatiotemporal cellular and molecular responses to complex tissue injury, interventions simulating clinically relevant flap complications (e.g., vascular thrombosis) as well as prophylactic, therapeutic or surgical treatment (e.g., flap delay) strategies in the presence or absence of confounding risk factors (e.g., substance abuse, irradiation, diabetes) or favorable wound-healing promoting activities (e.g., exercise). Detailed visual instructions in BEFAF protocol may serve as an aid for teaching medical or academic researchers basic vascular microsurgery techniques that focus on precision, tremor management and magnification.

Effects of cutaneous administration of an over-the-counter menthol cream during temperate-water immersion for exercise-induced hyperthermia in men

Introduction: Hyperthermia impairs various physiological functions and physical performance. We examined the effects of cutaneous administration with an over-the-counter (OTC) analgesic cream containing 20% methyl salicylate and 6% L-menthol during temperate-water immersion (TWI) for exercise-induced hyperthermia. Methods: In a randomized crossover design, twelve healthy males participated in both of two experiments. Firstly, participants underwent a 15-min TWI at 20°C with (CREAM) or without (CON) cutaneous application of an analgesic cream. Cutaneous vascular conductance (CVC) was measured using laser doppler flowmetry during TWI. In a subsequent experiment, same participants performed a 30-min strenuous interval exercise in a heated (35°C) environment to induce hyperthermia (~39°C), which was followed by 15 min of TWI. Results: Core body temperature, as measured by an ingestible telemetry sensor, and mean arterial pressure (MAP) were measured. CVC and %CVC (% baseline) were higher during TWI in CREAM than in CON (Condition effect: p = 0.0053 and p = 0.0010). An additional experiment revealed that core body heat loss during TWI was greater in CREAM than in CON (Cooling rate: CON 0.070 ± 0.020 vs. CREAM 0.084°C ± 0.026°C/min, p = 0.0039). A more attenuated MAP response was observed during TWI in CREAM than in CON (Condition effect: p = 0.0007). Conclusion: An OTC analgesic cream containing L-menthol and MS augmented cooling effects when cutaneously applied during TWI in exercise-induced hyperthermia. This was, at least in part, due to the counteractive vasodilatory effect of the analgesic cream. The cutaneous application of OTC analgesic cream may therefore provide a safe, accessible, and affordable means of enhancing the cooling effects of TWI.

Remodelling of the superficial vascular network of skin flaps in rats, following a vasodilatory cream application, before elevation

Flap necrosis on random pattern skin flaps continues to be a challenge. In this study, we evaluated whether topical application of a vasodilator substance (the prostaglandin PGI₂ analogue, Iloprost^®, in cream form) as pre-treatment, would increase blood flow and improve flap viability. Wistar rats randomly allocated into four groups with 7 rats per group and two flaps 4cm × 2cm in the same rat i.e. 56 flaps were developed. Flaps on the wright side received pre-treatment with Cream in different drug concentrations, 2.5μgr/gr, 5 μgr/gr, and 10μgr/gr and 20 μgr/gr containing the active factor Iloprost^®® ZK 36,374(M. W 360.5) prepared with white petrolatum as a base. Flaps on the left side received placebo cream (white petrolatum). After 10 days of flap pre-treatment, evaluation of blood flow by laser Doppler flowmetry (LDF) were recorded, then flap elevation and re suturing back were performed. After 7 days we estimated flap viability on digital imaging and the percentages of flap survival estimated. Means and standard deviations were used to describe blood flow measurements and survival percentages. The significance was set at 0.05 in all cases and the analysis were carried out with the use of the SPSS v23.0. Furthermore, we performed dynamic analyses of circulation using the radioisotope 99mTc which confirmed hyperaemia of the treated areas relative to that observed in control areas. These findings demonstrated that pretreatment of skin flaps with Iloprost^® cream for 10 days prior to elevation increased blood flow in the flap and improved their overall survival rate.

Topical Analgesic Containing Methyl Salicylate and L-Menthol Accelerates Heat Loss During Skin Cooling for Exercise-Induced Hyperthermia

Hyperthermia impairs physical performance and, when prolonged, results in heat stroke or other illnesses. While extensive research has investigated the effectiveness of various cooling strategies, including cold water immersion and ice-suit, there has been little work focused on overcoming the cutaneous vasoconstriction response to external cold stimulation, which can reduce the effectiveness of these treatments. Over-the-counter (OTC) topical analgesics have been utilized for the treatment of muscle pain for decades; however, to date no research has examined the possibility of taking advantage of their vasodilatory functions in the context of skin cooling. We tested whether an OTC analgesic cream containing 20% methyl salicylate and 6% L-menthol, known cutaneous vasodilators, applied to the skin during skin cooling accelerates heat loss in exercise-induced hyperthermia. Firstly, we found that cutaneous application of OTC topical analgesic cream can attenuate cold-induced vasoconstriction and enhance heat loss during local skin cooling. We also revealed that core body heat loss, as measured by an ingestible telemetry sensor, could be accelerated by cutaneous application of analgesic cream during ice-suit cooling in exercise-induced hyperthermia. A blunted blood pressure response was observed during cooling with the analgesic cream application. Given the safety profile and affordability of topical cutaneous analgesics containing vasodilatory agents, our results suggest that they can be an effective and practical tool for enhancing the cooling effects of skin cooling for hyperthermia.

Post-treatment with metformin improves random skin flap survival through promoting angiogenesis in rats

Skin flap necrosis has been remained as an unsolved problem in plastic and reconstructive surgeries. Here, we explored the effects of metformin post-treatment on random skin flap survival in rats. An 8.00 × 2.00 cm dorsal skin flap was created in 24 rats and they were then divided into three groups (n = 8) including Control, metformin (Met) 50.00 mg kg^-1 and Met 100 mg kg^-1. All animals were administrated orally until seven days after flap surgery. Flap survival, the number of blood vessels and mast cells in the flap tissues were analyzed. Vascular endothelial growth factor (VEGF) expression levels in flap tissues was also determined using immunohistochemical methods. The percentage of survival area in Met 50.00 mg kg^-1 and Met 100 mg kg^-1 groups were significantly higher compared to control. The blood vessel density and the VEGF positive cells in the viable areas of flaps showed a significant increase in Met 50.00 mg kg^-1 group compared to control group. The results of this study suggested that treatment with metformin, especially with low dose following skin flap surgery was effective in improving the flap survival and increasing the neovascularization in the flaps tissues of rats.

Standardization of the Rat Dorsal Random Pattern (McFarlane) Flap Model and Evaluation of the Pharmacological Agents Aiming to Salvage Partial Flap Necrosis: A Systematic Review and a Meta-analysis

INTRODUCTION

Partial flap necrosis is a common complication after surgery. McFarlane flap model has been used for assessment of various agents' effects on random flap survival. The aim of this study was to review the methodology of studies using this flap model and reveal the most successful agents.

MATERIALS AND METHODS

PubMed, Scopus, and Web of Science databases were screened for words "McFarlane flap," "flap survival," and ("flap" and "rat") by using time limits between 1965 and 2019. A total of 71 original articles were reviewed. Dimensions and base (cranial/caudal) of the flap, treatment protocol, follow-up period, and survival rates were extracted. Modified survival rates were calculated. Coefficients of variation of cranial/caudally based control group flaps and most commonly used flap models were calculated to assess interstudy variability.

RESULTS

A total of 165 different treatment regimens were studied. One-hundred twelve regimens (67.9%) were found to increase flap survival. Most common flap dimensions were 9 cm × 3 cm, followed by 10 cm × 3 cm, 8 cm × 2 cm and 6 cm × 2 cm. Studies using caudally based flaps showed less interstudy variability, but survival rates were similar. Pentoxifylline, sildenafil, chlorpromazine, phenoxybenzamine, and phentolamine were reported to be successful in multiple studies.

CONCLUSIONS

There are numerous agents found to be effective for treatment of partial flap necrosis, but further clinical research is needed. To overcome standardization problems, use of commonly used flap dimensions with a caudal base and interpretation of results after 7 days of follow-up seems appropriate.

The outcomes of dexmedetomidine and calcitriol on flap viability

Purpose:

To evaluate protective effects of dexmedetomidine, calcitriol and their combination.

Methods:

Forty Wistar-albino rats were divided into 4 groups; group of Sham (Group Sham); group of dexmedetomidine (Group DEX); group of calcitriol (Group CAL) and group of dexmedetomidineandcalcitriol (Group DEX-CAL). Photographic analysis was used for macroscopic analysis and perfusion analyses were evaluated by scintigraphy. Additionally, tissue malondialdehyde (MDA) and total oxidant status (TOS) and total antioxidant activity (TAS) were recorded and oxidative stress index (OSI) was calculated. Each flap was assessed by histopathology.

Results:

Compared to Group Sham, the viable flap areas were higher in all treatment groups both by photographic image analyses and perfusion analyses (p<0.05). Group DEX-CAL had the highest viable flap percentage both in scintigraphic and photographic analyses; whereas Group Sham had the lowest viable flap percentage. Similarly, TAS and MDA levels were elevated and TOS levels were declined in all treatment groups compared to Group Sham (p<0.005). Histopathological analysis at flap demarcation zone confirmed neovascularization was significantly higher and edema, necrosis and inflammation were significantly lower in all treatment groups compared to Group Sham.

Conclusion:

The outcomes show that additional premedication with either dexmedetomidine or calcitriol or their combination reduces ischemia-reperfusion injury of flap area and show significant increase in the percentage of viable flap tissue.

Current Knowledge on the Vascular Effects of Menthol

Menthol is a monoterpene alcohol, widely used in several food and healthcare products for its particular odor and flavor. For some decades, menthol has been known to act on the vasculature directly in the endothelium and vascular smooth muscle, with recent studies showing that it also evokes an indirect vascular response via sensory fibers. The mechanisms underlying menthol's vascular action are complex due to the diversity of cellular targets, to the interplay between signaling pathways and to the variability in terms of response. Menthol can evoke either a perfusion increase or decrease in vivo in different vascular territories, an observation that warrants a critical discussion. Menthol vascular actions in vivo seem to depend on whether the vascular territory under analysis has been directly provoked with menthol or is located deep/distant to the application site. Menthol increases perfusion of directly provoked skin regions due to a complex interplay of increased nitric oxide (NO), endothelium-derived hyperpolarization factors (EDHFs) and sensory nerve responses. In non-provoked vascular beds menthol decreases perfusion which might be attributed to heat-conservation sympathetically-mediated vasoconstriction, although an increase in tissue evaporative heat loss due the formulation ethanol may also play a role. There is increasing evidence that several of menthol's cellular targets are involved in cardiovascular diseases, such as hypertension. Thus menthol and pharmacologically-similar drugs can play important preventive and therapeutic roles, which merits further investigation.

Tolerability of a green tea-based mouth rinse: A pilot study

Introduction

Mouth rinse containing essential oil is one of the most popular, over the counter dental products which has been promoted to have anti-inflammatory, anti-plaque and anti-microbial properties. An essential oil alcohol-free mouth rinse with green tea has been introduced recently and promoted for management of periodontitis and gingivitis. As the role of chlorhexidine gluconate (CHX) mouth rinse in management of periodontal disease has been evaluated previously, the aim of this study is to compare the tolerability of none-alcohol containing green tea-based (NAGT) mouth rinse with CHX mouth rinse.

Methods

Forty healthy subjects were enrolled in September 2018 at King Abdulaziz University and allocated randomly to two study arms: NAGT mouth rinse and chlorhexidine gluconate mouth rinse. Study subjects were instructed to follow the manufacturer instructions and rinse twice daily for two weeks. Collected data included age, gender, smoking history in addition to subjective assessment using a validated questionnaire. Intraoral clinical examination was completed at baseline and 2-weeks time point.

Results

The data of 36 patients were included in this study and analyzed. At 2 weeks, NAGT group reported higher burning sensation score compared to chlorhexidine group (mean: 4.33 and 0.6 respectively; P < 0.05). Reported mucosal dryness was more evident in NAGT group (mean: 1.9 Vs 1.7 for chlorhexidine group). Oral examination revealed significant mucosal desquamation (27.8%) in NAGT group. However, oral ulceration was reported equally in both groups (5.6%).

Conclusion

The current data demonstrates an overall less tolerability of a non-alcohol containing green tea-based mouth rinse compared to chlorhexidine gluconate. Further long term randomized clinical trials are recommended to confirm our findings.

Effects of Asiaticoside Treatment on the Survival of Random Skin Flaps in Rats

Background: Asiaticoside (AS) is extracted from the traditional herbal medicine Centella asiatica, and has angiogenic, antioxidant, anti-inflammatory, and wound-healing effects. We investigated the effects of AS on skin flap survival. Methods: Dorsal McFarlane flaps were harvested from 36 rats and divided into two groups: an experimental group treated with 40 mg/kg AS administered orally once daily, and a control group administered normal saline in an identical manner. On day 2, superoxide dismutase (SOD) and malondialdehyde (MDA) levels, and production of the cytokines tumor necrosis factor-α and interleukin (IL)-6 were evaluated. On day 7, tissue slices were stained with hematoxylin and eosin. The expression of vascular endothelial growth factor (VEGF), IL-6, and IL-1β were immunohistochemically evaluated. Microcirculatory flow was measured using laser Doppler flowmetry. Flap angiography, using the lead oxide-gelatin injection technique, was performed with the aid of a soft X-ray machine. Results: The AS group exhibited greater mean flap survival area, improved microcirculatory flow, and higher expression levels of SOD and VEGF compared with the control group. However, MDA levels and the inflammatory response were significantly reduced. Conclusions: AS exhibits promise as a therapeutic option due to its effects on the viability and function of random skin flaps in rats.

An easy access to topical gels of an anti-cancer prodrug (5-fluorouracil acetic acid) for self-drug-delivery applications

An easy access to topical gels (both hydro- and organogels) derived from an anti-cancer prodrug namely 5-fluorouracil acetic acid (5-FuA) achieved by exploiting a simple salt formation strategy is reported for the first time.

Favorable effects of progesterone on skin random flap survival in rats

OBJECTIVES

The aim of this study is to determine the effects of progesterone treatment on the survival of random skin flaps.

MATERIALS AND METHODS

McFarlane flaps were established and 40 male rats were randomly assigned to the progesterone-treated as the test group or normal saline-treated as the control group. Progesterone or normal saline (10 mg/kg) was administered intraperitoneally once daily. On postoperative day 2, malondialdehyde (MDA) and superoxide dismutase (SOD) were detected using test kits. Flap survival rates were evaluated with transparent graph paper under direct visualization, the levels of inflammation were examined by haematoxylin and eosin (H&E) staining, and the expression of vascular endothelial growth factor (VEGF) was immunohistochemically evaluated on day 7.

RESULTS

Compared to that in the control group, the mean survival area was significantly larger in the progesterone group. SOD activity was increased significantly, but the MDA levels in the test group were decreased. H&E-stained slices revealed that inflammation was inhibited in the test group. VEGF expression markedly increased in the progesterone group.

CONCLUSION

This study showed that progesterone administered intraperitoneally significantly improved random skin flap survival in rats.

The Effect of Red Ginseng Extract Intake on Ischemic Flaps

Red ginseng is well known for its angiogenic effects and its effect of increasing expression of vascular endothelial growth factors (VEGFs), but little experimental evidence has been published. In this study, we examined the effect of red ginseng using an ischemic flap model. Twenty male Sprague-Dawley rats were divided into two groups of 10. One group drank red ginseng solution from 7 days prior to surgery to 7 days after, whereas the other group drank distilled water. We created a local flap on the back of each rat. We analyzed the surviving area of the flap for 10 days after surgery and measured the blood flow of the flap. Ten days after the operation, CD31-positive vessels and VEGF expression were examined by immunohistochemistry. The percentages of surviving areas of the flap were 76 ± 3% for the experimental group and 39 ± 5% for the control group (P = 0.0002). Blood flow in the experimental group increased for 10 days after the surgery. The number of newly generated capillaries in the experimental group was 14.0 ± 3.5, which was significantly higher than 5.7 ± 1.9 in the control group. The expression of VEGF in the experimental group was significantly higher than in the control group (p = 0.0003). Administration of red ginseng extract increases the survival of ischemic flaps via angiogenesis and elevated blood flow. Further clinical studies are warranted to apply the effect shown in this current investigation to various ischemic conditions.