A quantitative, non-invasive method for the characterization of flushing reactions

Measuring niacin-associated skin toxicity (NASTy) stigmata along with symptoms to aid development of niacin mimetics

Though cardioprotective, niacin monotherapy is limited by unpleasant cutaneous symptoms mimicking dermatitis: niacin-associated skin toxicity (NASTy). Niacin is prototypical of several emerging drugs suffering off-target rubefacient properties whereby agonizing the GPR109A receptor on cutaneous immune cells provokes vasodilation, prompting skin plethora and rubor, as well as dolor, tumor, and calor, and systemically, heat loss, frigor, chills, and rigors. Typically, NASTy effects are described by subjective patient-reported perception, at best semi-quantitative and bias-prone. Conversely, objective, quantitative, and unbiased methods measuring NASTy stigmata would facilitate research to abolish them, motivating development of several objective methods. In early drug development, such methods might better predict clinical tolerability in larger clinical trials. Measuring cutaneous stigmata may also aid investigations of vasospastic, ischemic, and inflammatory skin conditions. We present methods to measure NASTy physical stigmata to facilitate research into novel niacin mimetics/analogs, detailing characteristics of each technique following niacin, and how NASTy stigmata relate to symptom perception. We gave niacin orally and measured rubor by colorimetry and white-light spectroscopy, plethora by laser Doppler flowmetry, and calor/frigor by thermometry. Surprisingly, each stigma's abruptness predicted symptom perception, whereas peak intensity did not. These methods are adaptable to study other rubefacient drugs or dermatologic and vascular disorders.

Cutaneous responses to topical methyl nicotinate in black, oriental, and caucasian subjects

The response of human skin to topical methyl nicotinate (MN) has been monitored in black, oriental, and caucasian subjects. The study aimed to address the question: "Do racial differences in percutaneous absorption and microcirculatory sensitivity exist?" MN-induced vasodilatation was assessed visually and by laser Doppler velocimetry (LDV). At three dose levels, in the three subject populations, four parameters were compared: (a) the diameter of the maximum visually perceptible erythematous area (Emx); (b) the area under the erythematous diameter versus time curve (AUE); (c) the maximum LDV response (Lmax); and (d) the area under the LDV response versus time curve (AUL). At p less than 0.05, AUL (black) greater than AUL (caucasian) for all MN concentrations; AUL (oriental) greater than AUL (caucasian) for the higher dose levels. Emx, AUE and Lmx showed no significant differences between races within concentrations. For all subjects, Emx, AUE, and AUL were significantly dependent on MN dose whereas Lmx was not. The results suggest that some racial differences in response to topical MN exist and that perception of these distinctions may depend upon the method of measurement.

Rosacea: disturbed defense against brain overheating

Tympanic (Tty), esophageal (Tes), forehead, and hand skin temperatures, as well as the forehead evaporation rate were recorded in six men (four suffering from rosacea and two healthy controls) before, during, and after 1 h of warm bath (38 degrees-39 degrees C). During the last 30 min of the bath, the subject's face was vigorously fanned (14 m/s). Blood flow was explored with ultrasonic Doppler in the emissary veins of the cranium during normothermia before entering the bath, and during hyperthermia just after leaving it. Under normothermic conditions, Tty was higher than Tes in all subjects. In three patients, no blood flow could be detected in the ophthalmic emissary veins whereas in the fourth patient as well as in both control subjects, blood flowed from the intracranium to the face. During hyperthermia, face fanning decreased Tty by 0.25 degrees +/- 0.05 degrees C (+/- SEM) below Tes in the control subjects whereas in all patients Tty remained warmer than Tes by 0.1 degrees C. Doppler recordings showed a rapid inward blood flow from the skin to the brain in the controls during hyperthermia. In patients, however, there was no change from normothermia in the blood flow patterns of vena angularis oculi. Their forehead temperature was permanently higher than in control subjects. Venous blood flow from the skin to the brain appears to be suppressed in rosacea, thus inhibiting selective brain cooling in hyperthermic conditions. The importance of this mechanism in the pathogenesis of rosacea and its significance as a means of investigation are discussed.

Does monosodium glutamate cause flushing (or merely "glutamania")?

Monosodium glutamate is widely regarded as the provocative agent in the "Chinese restaurant syndrome," of which flushing is regarded as part of the reaction. Six subjects were monitored by laser Doppler velocimetry for changes in facial cutaneous blood flow during challenge with monosodium glutamate and its cyclization product, pyroglutamate. Additionally, records of patients challenged with monosodium glutamate in the laboratory were reviewed. No flushing was provoked among the twenty-four people tested, eighteen of whom gave a positive history of Chinese restaurant syndrome flushing. These results indicate that monosodium glutamate-provoked flushing, if it exists at all, must be rare. Monosodium glutamate and its cyclization product, pyroglutamate, may provoke edema and associated symptoms.

Cutaneous vascular sensitivity to lower aliphatic alcohols and aldehydes in Orientals

An ethnic predisposition to ethanol-provoked flushing among diverse Mongoloid populations may be the consequence of a delayed oxidation and accumulation of acetaldehyde. Orientals who flush after oral alcohol are more likely to have cutaneous erythema after topical ethanol or propanol, and the cutaneous vascular reaction to primary alcohols is actually provoked by the corresponding aldehyde. The cutaneous reaction to primary alcohols can be totally blocked by pretreatment with 4-methylpyrazole, a potent inhibitor of alcohol dehydrogenase.