Minoxidil exerts different inhibitory effects on gene expression of lysyl hydroxylase 1, 2, and 3: implications for collagen cross-linking and treatment of fibrosis

Collagen deposits in fibrotic lesions often display elevated levels of hydroxyallysine (pyridinoline) cross-links. The relation between the occurrence of pyridinoline cross-links and the irreversibility of fibrosis suggests that these cross-links contribute to the aberrant accumulation of collagen. Based on its inhibitory effect on lysyl hydroxylase activity minoxidil has been postulated to possess anti-fibrotic properties by limiting the hydroxylysine supply for hydroxyallysine cross-linking. However, to interfere with hydroxyallysine cross-linking specifically lysyl hydroxylation of the collagen telopeptide should be inhibited, a reaction predominantly catalysed by lysyl hydroxylase (LH) 2b. In this study, we demonstrate that minoxidil treatment of cultured fibroblasts reduces LH1>>LH2b>LH3 mRNA levels dose-and time-dependently, but has essentially no effect on the total number of pyridinoline cross-links in the collagen matrix. Still the collagen produced in the presence of minoxidil displays some remarkable features: hydroxylation of triple helical lysine residues is reduced to 50% and lysylpyridinoline cross-linking is increased at the expense of hydroxylysylpyridinoline cross-linking. These observations can be explained by our finding that LH1 mRNA levels are the most sensitive to minoxidil treatment, corroborating that LH1 has a preference for triple helical lysine residues as substrate. In addition, the non-proportional increase in cross-links (20-fold) with respect to the decrease in lysyl hydroxylation state of the triple helix (2-fold) even suggests that LH1 preferentially hydroxylates triple helical lysine residues at the cross-link positions. We conclude that minoxidil is unlikely to serve as an anti-fibroticum, but confers features to the collagen matrix, which provide insight into the substrate specificity of LH1.

Is the sarcolemmal or mitochondrial K(ATP) channel activation important in the antiarrhythmic and cardioprotective effects during acute ischemia/reperfusion in the intact anesthetized rabbit model?

The relative contributions of cardiomyocyte sarcolemmal ATP-sensitive K(+) (K(ATP)) and mitochondrial K(ATP) channels in the cardioprotection and antiarrhythmic activity induced by K(ATP) channel openers remain obscure, though the mitochondrial K(ATP) channels have been proposed to be involved as a subcellular mediator in cardioprotection afforded by ischemic preconditioning. In the present study, we sought to investigate the effects of administration of ATP-sensitive K(+) channel (K(ATP)) openers (nicorandil and minoxidil), a specific mitochondrial K(ATP) channel blocker (5-hydroxydecanoate (5-HD)) and a specific sarcolemmal K(ATP) channel blocker (HMR 1883; (1-[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3-methylthiourea) prior to coronary occlusion as well as prior to post-ischemic reperfusion on survival rate, ischemia-induced and reperfusion-induced arrhythmias and myocardial infarct size in anesthetized albino rabbits. The thorax was opened in the left 4th intercostal space and after pericardiotomy the heart was exposed. In Group I (n=88), occlusion of the left main coronary artery and hence, myocardial ischemia-induced arrhythmias was achieved by tightening a previously placed loose silk ligature for 30 min. In Group II (n=206), arrhythmias were induced by reperfusion following a 20-min ligation of the left main coronary artery. Both in Group I and Group II, intravenous (i.v.) administration of nicorandil (0.47 mg/kg), minoxidil (0.5 mg/kg), HMR 1883 (3 mg/kg)/nicorandil and HMR 1883 (3 mg/kg)/minoxidil before coronary artery occlusion increased survival rate (86%, 75%, 75% and 86% vs. 55% in the control subgroup in Group I; 75%, 67%, 67% and 75% vs. 46% in the control subgroup in Group II), significantly decreased the incidence and severity of life-threatening arrhythmias. In Group II, i.v. administration of nicorandil and minoxidil before coronary artery occlusion significantly decreased myocardial infarct size. However, i.v. administration of nicorandil or minoxidil before reperfusion did neither increase survival rate nor confer any antiarrhythmic or cardioprotective effects. The antiarrhythmic and cardioprotective effects of both nicorandil and minoxidil were abolished by pretreating the rabbits with 5-HD (5 mg/kg, i.v. bolus), a selective mitochondrial K(ATP) channel blocker but not by HMR 1883 (3 mg/kg). In the present study, higher levels of malondialdehyde (MDA) and lower levels of reduced glutathione (GSH) and superoxide dismutase (SOD) in necrotic zone of myocardium in all the 16 subgroups in Group II suggest little anti-free radical property of nicorandil and minoxidil. We conclude that intervention by intravenous administration of nicorandil and minoxidil (through the selective activation of mitochondrial K(ATP) channels) increased survival rate and exhibited antiarrhythmic and cardioprotective effects during coronary occlusion and reperfusion in anesthetized rabbits when administered prior to coronary occlusion. The cardiomyocyte mitochondrial K(ATP) channel may be a pharmacologically modulable target of cardioprotection and antiarrhythmic activity.

Development and validation of a procedure for the determination of minoxidil in hair-regrowth formulations using two variants of capillary zone electrophoresis

A high performance capillary electrophoresis method was developed and validated for purity assessment of minoxidil bulk drug and for determination of minoxidil in Rogaine. The principal use of the method was in analyzing illicit minoxidil-containing hair-regrowth samples. Although validated for Rogaine, the procedure proved equally viable on illicit minoxidil-containing preparations. The developed method fulfilled the goal of providing an orthogonal technique to HPLC for confirmation of the presence of minoxidil in these imitations. The method was validated on two instruments, one utilizing EK injection, the other gravity injection. It is selective for minoxidil, which is separated from known process impurities and the single degradation impurity. Validation figures of merit for linearity/recovery (accuracy) and precision were in accordance with current expectations for method validation.

Limitations of human occipital scalp hair follicle organ culture for studying the effects of minoxidil as a hair growth enhancer

Minoxidil induces new hair growth in approximately one-third of patients with androgenetic alopecia after 1 year of treatment. With several conflicting reports in the literature based on small-scale studies, the current study aimed to clarify whether organ culture of human scalp anagen VI hair follicles is a suitable in vitro test system for reproducing, and experimentally dissecting, the recognized in vivo hair-growth-promoting capacity of minoxidil. Hair shaft elongation was studied in terminal anagen VI hair follicles microdissected from the occipital scalp of 36 healthy adults. A total of 2300 hair follicles, approximately 65 per individual, were tested using modifications of a basic organ culture protocol. It is shown here that minoxidil does not significantly increase hair shaft elongation or the duration of anagen VI in ex vivo culture despite several enhancements on the conventional methodology. This disparity to what is seen clinically in minoxidil responders may be explained by the following: (i) use of occipital (rather than frontotemporal or vertex) hair follicles; (ii) use of, already maximally growing, anagen VI hair follicles; (iii) a predominance of hair follicles from minoxidil unresponsive-donors; (iv) use of minoxidil rather than its sulfate metabolite; and/or (v) use of a suboptimal minoxidil dosage. This disparity questions the usefulness of standard human hair follicle organ culture in minoxidil research. Unexpectedly, minoxidil even inhibited hair shaft elongation in the absence of insulin, which may indicate that the actual hair-growth-modulatory effects of minoxidil depend on the concomitant local presence/absence of other growth modulators.

Novel and Established Potassium Channel Openers Stimulate Hair Growth In Vitro: Implications for their Modes of Action in Hair Follicles

Although ATP-sensitive potassium (K(ATP)) channel openers, e.g., minoxidil and diazoxide, can induce hair growth, their mechanisms require clarification. Improved drugs are needed clinically. but the absence of a good bioassay hampers research. K(ATP) channels from various tissues contain subtypes of the regulatory sulfonylurea receptor, SUR, and pore-forming, K(+) inward rectifier subunits, Kir6.X, giving differing sensitivities to regulators. Therefore, the in vitro effects of established potassium channel openers and inhibitors (tolbutamide and glibenclamide), plus a novel, selective Kir6.2/SUR1 opener, NNC 55-0118, were assessed on deer hair follicle growth in serum-free median without streptomycin. Minoxidil (0.1-100 microM, p<0.001), NNC 55-0118 (1 mM, p<0.01; 0.1, 10, 100 microM, p<0.001), and diazoxide (10 microM, p<0.01) increased growth. Tolbutamide (1 mM) inhibited growth (p<0.001) and abolished the effect of 10 microM minoxidil, diazoxide and NNC 55-0118; glibenclamide (10 microM) had no effect, but prevented stimulation by 10 microM minoxidil. Phenol red stimulated growth (p<0.001), but channel modulator responses remained unaltered. Thus, deer follicles offer a practical, ethically advantageous in vitro bioassay that reflects clinical responses in vivo. The results indicate direct actions of K(ATP) channel modulators within hair follicles via two types of channels, with SUR 1 and SUR 2, probably SUR2B, sulfonylurea receptors.

Minoxidil, a K(ATP) channel opener, accelerates DNA synthesis following partial hepatectomy in rats

A large number of studies have reported the action of K(ATP) channel openers in accelerating the proliferation of hepatocytes and many other cell types in vitro. Few studies, however, have examined the proliferative effect of K(ATP) channel openers in vivo. The aim of this study was to determine whether the K(ATP) channel opener minoxidil accelerates liver regeneration after partial hepatectomy (PH) in vivo. Male Wistar rats underwent a 70% partial hepatectomy (PH) after receiving a subcutaneous injection of minoxidil (0.01 mg/kg or 0.03 mg/kg). Some of the rats were intravenously treated with 5-hydroxydecanoic acid (5-HD, 10 mg/kg) just before the minoxidil injection. Seventy-two hours after PH, DNA synthesis was immunohistochemically assessed by bromodeoxyuridine (BrdU) incorporation into the nuclei. Minoxidil induced significant and dose-dependent increase in the BrdU labeling index after PH, and 5-HD reversed this minoxidil-induced change. Minoxidil did not significantly affect the changes in liver weight and liver function after PH. The hepatic levels of prealbumin decreased by about 60% after PH and minoxidil inhibited the decrease. In conclusion, the K(ATP) channel opener minoxidil enhanced DNA synthesis after PH without affecting the liver function.

Effect of minoxidil on proliferation and apoptosis in dermal papilla cells of human hair follicle

BACKGROUND

Minoxidil has been widely used to treat androgenetic alopecia, but little is known about its pharmacological activity or about the identity of its target cells in hair follicles. We hypothesized that minoxidil has direct effects on the proliferation and apoptosis of dermal papilla cells (DPCs) of human hair follicle.

OBJECTIVE

To elucidate the mechanism of topical minoxidil action in terms of stimulating hair growth.

METHODS

We evaluated cell proliferations in cultured DPCs by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and measured the expressions of extracellular signal-regulated kinase (ERK), Akt, Bcl-2, and Bax by Western blot. We also measured elongation of hair follicles in organ culture.

RESULTS

Minoxidil significantly increased the proliferation of DPCs. The levels of ERK phosphorylation and of phosphorylated Akt increased significantly 1 h post-treatment; percentage increase of ERK phosphorylation was 287% at 0.1 microM and 351% at 1.0 microM of minoxidil, and that of Akt phosphorylation was 168% at 0.1 microM and 257% at 1.0 microM of minoxidil. 1.0 microM of minoxidil increased Bcl-2 expression over 150%, while 1.0 microM of minoxidil decreased Bax expression by more than 50%. Moreover, a significant elongation of individual hair follicles in organ culture was observed after adding minoxidil.

CONCLUSION

Minoxidil promotes the survival of human DPCs by activating both ERK and Akt and by preventing cell death by increasing the ratio of Bcl-2/Bax. We suggest that minoxidil stimulates the growth of human hairs by prolonging anagen through these proliferative and anti-apoptotic effects on DPCs.

Minoxidil: an underused vasodilator for resistant or severe hypertension

Minoxidil is a direct vasodilator introduced in the early 1970s for the treatment of hypertension. It is capable of reducing blood pressure in most persons with resistant hypertension where therapy has failed with multidrug regimens. Minoxidil's effect can be limited because of an increase in pulse rate and/or sodium (and water) retention. The latter may prove quite debilitating in some patients. Thus, minoxidil is generally administered with both a diuretic and an agent that can keep pulse rate in check, such as a beta blocker or a combined alpha-beta blocker. The prominent tachycardia with minoxidil can aggravate myocardial ischemia and, if long-standing, leads to left ventricular hypertrophy. Minoxidil has a particularly annoying side effect of hypertrichosis that may limit its use, particularly among women. Minoxidil use is infrequently associated with the idiosyncratic onset of a pericardial effusion. If a patient's hypertension is severe enough to warrant minoxidil therapy, a hypertension specialist should probably become involved in the patient's care. The use of this medication should be limited in view of the availability of effective agents with fewer side effects. There is, however, a place for minoxidil in the treatment of resistant hypertension especially in patients with advanced renal disease.

Minoxidil Attenuates Ischemia-Induced Apoptosis in Cultured Neonatal Rat Cardiomyocytes

The effects of minoxidil (a mitochondrial K+(ATP) channel opener) on ischemia-induced necrosis and apoptosis were examined using a cardiomyocyte model of simulated ischemia, since mitochondrial K+(ATP) channel openers have been suggested to be involved in the mechanisms of cardioprotective action against ischemia/reperfusion injury. In the absence of minoxidil, simulated ischemia led to cellular release of creatine phosphokinase (CPK), morphologic degeneration, and beating cessation within 24 to 72 hours. Based on the Hoechst 33258 staining pattern, a significant number of cells placed in sealed flasks underwent apoptosis. Myocytes treated with 5 microM of minoxidil failed to alter the degree of ischemia-induced CPK loss for 48 to 72 hours. However, minoxidil treatment prevented the loss of beating function in many of the ischemic cells, and attenuated the decline in intracellular ATP content after a 48-hour ischemic incubation. The number of nuclear fragmentation was significantly reduced in minoxidil-treated cells after a 72-hour ischemic insult compared with untreated ischemic cells. This effect was blocked by the mitochondrial K+(ATP) channel antagonist 5-HD. The data suggest that minoxidil renders the cell resistant to ischemia-induced necrosis and apoptosis. The beneficial effects of minoxidil appear to be related to the opening of mitochondrial K+(ATP) channels.

Topical minoxidil counteracts stress-induced hair growth inhibition in mice

Stress has long been suspected as a possible cause of hair loss in various species, even though convincing experimental evidence has not been available. Recently, we have shown in a murine model that sonic stress alters hair growth and cycling in vivo, and have postulated the existence of a 'brain-hair follicle axis' (BHA). In order to study whether a clinically available and widely used topically active hair growth stimulator mitigates stress-triggered hair growth inhibition in this stress model, we have applied a 5% minoxidil solution. Female CBA/J mice were depilated and randomized in to two groups: control (n = 20) and sonic stress (n = 20). These groups were further divided and either treated daily with 5% minoxidil solution or vehicle alone. The stress group was exposed to sonic stress for 24 h starting 14 days after anagen induction by depilation. All mice were sacrificed 16 days after the depilation and assessed by quantitative histomorphometry. Sonic stress significantly increased the number of hair follicles with apoptotic cells and inhibited intrafollicular keratinocyte proliferation. In addition, the number of clusters of perifollicular MHC class II+ cells and degranulated perifollicular mast cells was significantly enhanced in the stressed mice. In accordance with previous findings, all stressed mice showed an advanced hair cycle progression towards catagen. All of these stress-induced hair growth inhibitory changes along the BHA were down-regulated by topical minoxidil application. This encourages one to explore clinically whether topical minoxidil is a safe and effective pharmacologic tool for the management of stress-associated telogen effluvium in humans.

Minoxidil: mechanisms of action on hair growth

We have known for over 30 years that minoxidil stimulates hair growth, yet our understanding of its mechanism of action on the hair follicle is very limited. In animal studies, topical minoxidil shortens telogen, causing premature entry of resting hair follicles into anagen, and it probably has a similar action in humans. Minoxidil may also cause prolongation of anagen and increases hair follicle size. Orally administered minoxidil lowers blood pressure by relaxing vascular smooth muscle through the action of its sulphated metabolite, minoxidil sulphate, as an opener of sarcolemmal KATP channels. There is some evidence that the stimulatory effect of minoxidil on hair growth is also due to the opening of potassium channels by minoxidil sulphate, but this idea has been difficult to prove and to date there has been no clear demonstration that KATP channels are expressed in the hair follicle. A number of in vitro effects of minoxidil have been described in monocultures of various skin and hair follicle cell types including stimulation of cell proliferation, inhibition of collagen synthesis, and stimulation of vascular endothelial growth factor and prostaglandin synthesis. Some or all of these effects may be relevant to hair growth, but the application of results obtained in cell culture studies to the complex biology of the hair follicle is uncertain. In this article we review the current state of knowledge on the mode of action of minoxidil on hair growth and indicate lines of future research.

[Effects of NGF and estrogens on human hair follicle in vitro]

OBJECTIVE

To observe the effects of NGF, estrogens and minoxidil on the growth of human hair follicle in vitro.

METHODS

In a model of human hair follicle in vitro, the follicle was separately treated with the NGF, estrogens and minoxidil. The growth of the hair follicle was measured in length with an eyepiece micrometer. The effects of the NGF, estrogens and minoxidil were evaluated by measuring the rates of incorporation of 3H-TdR of DNA synthesis.

RESULTS

The growth of the human hair follicle was showing significantly faster in the 100 ng/ml NGF and 125 micrograms/ml minoxidil groups, compared with the control (P < 0.05), but the growth was significantly inhibited in the 0.5 microgram/ml 17 beta-E2 group (P < 0.05). There was no difference shown for the growth of the hair follicle in the group mixed with 100 ng/ml NGF and 0.5 microgram/ml 17 beta-E2 (P > 0.05). The rates of incorporation of 3H-TdR in the groups were shown that the results just correlated with the results of the above-mentioned method.

CONCLUSIONS

The 100 ng/ml NGF and 125 micrograms/ml minoxidil could increase the growth of human hair follicle while the 0.5 microgram/ml 17 beta-E2 could inhibit it. The 100 ng/ml NGF could neutralized the effect of the 0.5 microgram/ml 17 beta-E2.

Effect of potassium channel modulators on toxicity of Cleistanthus collinus

The study was conducted to determine the effects of boiled extract of Cleistanthus collinus on rats by observing ECG changes and electrolyte levels in serum and urine. Influence of minoxidil and glibenclamide on Cleistanthus collinus induced toxicity was determined. ED50 for arrhythmia, changes in contractility and heart rate were recorded using the isolated frog heart. Cleistanthus at low doses caused transient tachycardia and increase in contractility and at high dose caused arrhythmia and cardiac arrest in rat. LD50 was found to be 1690 mg/kg. Minoxidil potentiated cardiac toxicity, whereas glibenclamide did not produce any significant change. High concentration of potassium in Cleistanthus extract hindered comparison of its levels. There was excretion of sodium even in the presence of hyponatraemia. Cleistanthus at low dose caused transient tachycardia and increase in contractility and at high dose caused arrhythmia and cardiac arrest in isolated frog heart. ED50 for arrhythmia was found to be 1406 mg/kg. Acute toxicity was mainly due to depressive cardiac activity of Cleistanthus. It also caused renal failure. Potassium channel modulators did not have important role in acute cardiac toxicity treatment. Probably in chronic toxicity, electrolyte level changes are involved and potassium channel modulators might have a role.

Minoxidil opens mitochondrial K(ATP) channels and confers cardioprotection

1. ATP-sensitive potassium channel in the mitochondrial inner membrane (mitoK(ATP) channel) rather than in the sarcolemma (sarcK(ATP) channel) appears to play an important role in cardioprotection. We examined the effect of minoxidil, a potent antihypertensive agent and hair growth stimulator, on sarcK(ATP) and mitoK(ATP) channels in guinea-pig ventricular myocytes. 2. Minoxidil activated a glybenclamide-sensitive sarcK(ATP) channel current in the whole-cell recording mode with an EC(50) of 182.6 microm. Minoxidil reversibly increased the flavoprotein oxidation, an index of mitoK(ATP) channel activity, in a concentration-dependent manner. The EC(50) for mitoK(ATP) channel activation was estimated to be 7.3 microm; this value was notably approximately 25-fold lower than that for sarcK(ATP) channel activation. 3. Minoxidil (10 microm) significantly attenuated the ouabain-induced increase of mitochondrial Ca(2+) concentration, which was measured by loading cells with rhod-2 fluorescence. Furthermore, pretreatment with minoxidil (10 microm) before 20-min no-flow ischaemia significantly improved the recovery of developed tension measured after 60 min of reperfusion in coronary perfused guinea-pig ventricular muscles. These cardioprotective effects of minoxidil were completely abolished by the mitoK(ATP) channel blocker 5-hydroxydecanoate (500 microm). 4. Our results indicate that minoxidil exerts a direct cardioprotective effect on heart muscle cells, an effect mediated by the selective activation of mitoK(ATP) channels.

Adenosine 5'-triphosphate-sensitive potassium channel-mediated blood-brain tumor barrier permeability increase in a rat brain tumor model

Brain tumor microvessels/capillaries limit drug delivery to tumors by forming a blood-brain tumor barrier (BTB). The BTB overexpresses ATP-sensitive potassium (K(ATP)) channels that are barely detectable in normal brain capillaries, and which were targeted for BTB permeability modulation. In a rat brain tumor model, we infused minoxidil sulfate (MS), a selective K(ATP) channel activator, to obtain sustained, enhanced, and selective drug delivery, including various sized molecules, across the BTB to brain tumors. Glibenclamide, a selective K(ATP) channel inhibitor, significantly attenuated the MS-induced BTB permeability increase. Immunocytochemistry and glibenclamide binding studies showed increased K(ATP) channel density distribution on tumor cells and tumor capillary endothelium, which was confirmed by K(ATP) channel potentiometric assay in tumor cells and brain endothelial cells cocultured with brain tumor cells. MS infusion in rats with brain tumors significantly increased transport vesicle density in tumor capillary endothelial and tumor cells. MS facilitated increased delivery of macromolecules, including Her-2 antibody, adenoviral-green fluorescent protein, and carboplatin, to brain tumors, with carboplatin significantly increasing survival in brain tumor-bearing rats. K(ATP) channel-mediated BTB permeability increase was also demonstrated in a human, brain tumor xenograft model. We conclude that K(ATP) channels are a potential target for biochemical modulation of BTB permeability to increase antineoplastic drug delivery selectively to brain tumors.

Activity of potassium channel-blockers in breast cancer

BACKGROUND

Potassium ion (K+) channels are known to play a key role in breast cancer proliferation.

MATERIALS AND METHODS

We investigated the expression of Kv1.3 voltage-gated K+ channels in 60 human breast cancer specimens by immunohistochemistry. The effects of K+ channel-blockers on cellular proliferation were examined in vitro.

RESULTS

No immunostaining was observed in 4 normal human breast specimens. Eighteen (30%) breast cancer specimens showed high, 35 (58%) moderate and 7 (12%) low Kv1.3 staining in the epithelial compartment. Minoxidil (K+ channel-opener) stimulated growth of MCF-7 human breast cancer cells (maximal approximately 60% at 10 micrograms/mL). K+ channel-blockers, dequalinium and amiodarone, had marked inhibitory effects on MCF-7 proliferation (> 90% inhibition at 1.5 micrograms/mL). Importantly, amiodarone and dequalinium potentiated the growth-inhibitory effects of tamoxifen on human breast (MCF-7, MDA-MB-231) as well as prostate (PC3, MDA-PCA-2B) and colon (Colo320DM, SW1116) cancer cell lines.

CONCLUSION

Investigation of combination therapy with tamoxifen and K+ channel-blockers is warranted.

Effect of angiotensin AT2 receptor stimulation on vascular cyclic GMP production in normotensive Wistar Kyoto rats

In the present study in normotensive Wistar Kyoto rats (WKY), we investigated whether any angiotensin II (ANG II) increases in vascular cyclic GMP production were via stimulation of AT(2) receptors. Adult WKY were infused for 4h with ANG II (30 ng/kg per min, i.v.) or vehicle (0.9% NaCl, i.v.) after pretreatment with (1) vehicle, (2) losartan (100 mg/kg p.o.), (3) PD 123319 (30 mg/kg i.v.), (4) losartan+PD 123319, (5) icatibant (500 microg/kg i.v.), (6) L-NAME (1 mg/kg i.v.), (7) minoxidil (3 mg/kg i.v.). Mean arterial blood pressure (MAP) was continuously monitored, and plasma ANG II and aortic cyclic GMP were measured at the end of the study. ANG II infusion over 4h raised MAP by a mean of 13 mmHg. This effect was completely prevented by AT(1) receptor blockade. PD 123319 slightly attenuated the pressor effect induced by ANG II alone (123.4+/-0.8 versus 130.6+/-0.6) but did not alter MAP in rats treated simultaneously with ANG II + losartan (113+/-0.6 versus 114.3+/-0.8). Plasma levels of ANG II were increased 2.2-3.7-fold by ANG II infusion alone or ANG II in combination with the various drugs. The increase in plasma ANG II levels was most pronounced after ANG II+losartan treatment but absent in rats treated with losartan alone. Aortic cyclic GMP levels were not significantly changed by either treatment. Our results demonstrate that the AT(2) receptor did not contribute to the cyclic GMP production in the vascular wall of normotensive WKY.

The effects of the potassium channel opener minoxidil on renal electrolytes transport in the loop of henle

ATP-sensitive potassium channels (K(ATP)) in the thick ascending limb of the loop of Henle play an important role in apical K(+) recycling, a mechanism essential for maintaining the activity of the Na/2Cl/K-cotransporter. We have previously demonstrated that inhibition of K(ATP) decreases Na(+) and K(+) absorption in the loop of Henle and induces diuretic and natriuretic effects. In the present study, we used renal clearance and in vivo microperfusion techniques to evaluate the effects of the K(ATP) opener minoxidil on the urinary excretion and absorption in the loop of Henle of Na(+), K(+), Ca(2+), and Mg(2+). Intravenous injection of minoxidil (1.5 mg/kg) significantly decreased fractional Na(+) (FENa) and Mg(2+) (FEMg) excretion and urine volume with a moderate decrease in blood pressure (12%) and glomerular filtration rate (15%). Urine volume decreased 63%, and FENa and FEMg decreased 58 and 37%, respectively. In contrast, K(+) and Ca(2+) excretion did not change significantly. In the microperfusion of the loop of Henle, addition of minoxidil to the perfusion fluid significantly increased fluid (J(v)), Na(+) (J(Na)), Cl(-) (J(Cl)), and K(+) (J(K)) absorption. J(v) increased 44% (from 8.32 to 11.95 nl/min), J(Na) increased 14% (from 1.96 to 2.34 nmol/min), J(Cl) increased 21% (from 1.72 to 2.08 nmol/min), and J(K) increased 57% (from 35.8 to 56.4 pmol/min). We conclude that the activation of K(ATP) leads to stimulation of Na/2Cl/K-cotransporter activity and increases the rates of Na(+), Cl(-), and K(+) absorption in the loop of Henle, an effect contributing to the antidiuretic and antinatriuretic action of this K channel opener.

Expression and activity of potassium ion channels in human prostate cancer

Four normal and 79 human prostate cancer (Pca) specimens were examined, by immunohistochemistry, for expression of voltage-gated potassium ion channels. Strong immunostaining (for Kv1.3) was observed in the normal and 47% (37/79) of Pca specimens. Twenty-nine percent (23/79) Pca specimens showed moderate and 24% (19/79) displayed low staining. Three potassium channel-openers at a concentration of 10 microg/mL, minoxidil (47.8 microM), 1-Ethyl-2-benzimidazolinone (EBIO) (61.7 microM) and diazoxide (43.3 microM), increased growth of PC3 cells by 30-50%. Potassium channel-blockers, dequalinium, amiodarone and glibenclamide, caused a dose-dependent, growth inhibition of four human Pca cell lines. Apoptosis occurred within 4h of treatment of PC3 cells with dequalinium (0.5 microg/mL, 0.9 microM), amiodarone (5 microg/mL, 7.3 microM) or glibenclamide (50 microg/mL, 0.1mM).

The hydraulic influence in androgen-related hair growth: implications in autoimmune disease

Androgen-related changes in hair growth represent something of a mystery. Through the action of dihydrotestosterone (DHT), hair growth is increased in specific areas of the body. Elevated levels of DHT produce a general increase over the larger part of the body, often accompanied by hair loss in specific areas of the scalp. Because of this 'opposite' effect, a genetic difference in the hair follicles is proposed. This view is supported through the success of the 'plug graft' transplantation technique. However, this is unsatisfactory, because transplantation procedures that should work well according to this theory, ultimately fail. There is an alternative 'mechanism', that demonstrates its origins in the prime function of hair as an insulator. This simple mechanism makes sense of all the recognized effects of DHT in the dermal system, and throughout the body. In DHT-related hair growth it can be directly observed. The implication is that DHT achieves its effects through a primary physiological action that can be easily tested given the necessary expertise. Given existing knowledge, such a proven action of DHT would have serious implications for further understanding of female susceptibility to autoimmune disease.

Polyphenols from the heartwood of Cercidiphyllum japonicum and their effects on proliferation of mouse hair epithelial cells

The methanol extract of heartwood of Cercidiphyllum japonicum (Cercidiphyllaceae) stimulated proliferation of mouse hair epithelial cells, similar to minoxidil and procyanidin B-2. (+)-Taxifolin ( 2), quercetin ( 3), myricetin ( 4), (+)-dihydromyricetin ( 5) and gallic acid ( 6) were isolated from C. japonicum and showed significant proliferative activities on the hair epithelial cells.

Effects of minoxidil on ischemia-induced mechanical and metabolic dysfunction in dog myocardium

Effects of minoxidil on ischemia-induced myocardial mechanical and metabolic dysfunction were examined in anesthetized open-chest dogs. A regional portion of the left ventricle was made ischemic for 20 min by ligating the left anterior descending coronary artery, and then reperfused for 120 min. Dimethylsulfoxide or minoxidil (0.3, or 1.0 mg/kg) was injected intravenously 10 min before ligation. Ischemia decreased regional myocardial contraction, and reperfusion recovered it but incompletely. Myocardial metabolic derangement was observed during ischemia, such as decreases in the myocardial levels of ATP and creatine phosphate. These metabolic changes caused by ischemia were restored by reperfusion. Minoxidil injection at 0.3 and 1.0 mg/kg significantly decreased blood pressures but increased coronary flow. Pretreatment with minoxidil significantly enhanced the recovery of myocardial contraction during reperfusion after ischemia. The levels of ATP and creatine phosphate in the ischemic myocardium were significantly preserved by minoxidil at 0.3 mg/kg. No significant effect of minoxidil on the metabolism was observed in the 120 min reperfused myocardium. In conclusion, minoxidil improved the mechanical dysfunction in the reperfused heart and the drug at low dose preserved high-energy phosphates during ischemia.

Voltage-gated potassium ion channels in colon cancer

Voltage-gated potassium channels (VGPCs) have been previously implicated in cellular proliferation. In this study, the expression of VGPCs was examined by immunohistochemistry in seventy-four human colonic carcinoma specimens. Immunostaining for the Kv1.3 type VGPC was absent in two normal human colon specimens. Kv1.3 staining in the 74 colon cancer specimens was low in 9% (7/74), moderate in 61% (45/74) and high in 30% (22/74). Potassium channel (PC) openers, minoxidil and diazoxide (5-50 microg/ml), increased growth of SW1116, LoVo, Colo320DM and LS174t human colon cancer cell lines by 20-40%. PC-blockers, dequalinium and amiodarone, caused marked growth-inhibition of the four cell lines, at concentrations between 1 to 3 microg/ml. PC-blockers such as glibenclamide inhibited cellular proliferation at concentrations above 50 microg/ml while tetraethylammonium and 4-aminopyridine (up to 100 microg/ml) did not have significant growth-suppressive effects. Our results indicate the presence of VGPCs in colon cancer and suggest that PCs could serve as therapeutic targets.

[Effectivity versus toxicity of minoxidil as antiproliferative agent for lens epithelial cells. In vitro study]

PURPOSE

To evaluate the inhibitory effect of minoxidil on cultured proliferating lens epithelial cells (LECs) versus cytotoxic effect over corneal endothelial cells in culture, because minimum side effects over anterior chamber structures and particularly on corneal endothelium are required for successful therapy and prevention of posterior capsular opacification (PCO).

METHODS

New Zealand Rabbit LECs and corneal endothelium were cultured in DMEM at 35 degrees C in 5% CO2 in multiwells during 7 days. Both types of cells were exposed to minoxidil (1, 2 and 4 mM) for 1 and 24 hours. Control group and balanced salt solution group were included. After seven days multiwells were processed for light microscopy study. Morphometric study of cellular population of LECs and corneal endothelium cells were done using a computed planimetry system.

RESULTS

Dose-dependent effect on LECs proliferation was noted and non-confluent colonies of cells were observed on all treated groups. Morphologic changes in normal appearance of corneal endothelial cells after 1 hour of minoxidil treatment was observed and intracellular alterations were confirmed even with the lowest dose exposure.

CONCLUSIONS

Although effectiveness of minoxidil suppressing in vitro LECs proliferation could be suggest as a useful therapeutic agent to prevent PCO, however the inhibitory effect of different concentrations on corneal endothelial cells conditioned its possible use on ocular surgery.

[Hair growth effect of minoxidil]

The length and size of hair are depend on the anagen term in its hair cycle. It has been reported that the some cell growth factors, such as VEGF, FGF-5S, IGF-1 and KGF, induce the proliferation of cells in the matrix, dermal papilla and dermal papillary vascular system and increase the amount of extra cellular matrix in dermal papilla and then maintain follicles in the anagen phase. On the other hand, negative factors, like FGF-5, thrombospondin, or still unknown ones, terminate the anagen phase. If the negative factors become dominant against cell proliferation factors according to fulfilling some time set by the biological clock for hair follicles, TGF beta induced in the matrix tissues evokes apoptosis of matrix cells and shifts the follicles from anagen to catagen. Androgenetic alopecia is caused by miniaturizing of hair follicles located in the frontal or crown part of scalp and are hereditarily more sensitive to androgen. In their hair cycles, the androgen shortens the anagen phase of follicles and shifts them to the catagen phase earlier than usual. The mode of action of hair growth effect of minoxidil is not completely elucidated, but the most plausible explanation proposed here is that minoxidil works as a sulfonylurea receptor (SUR) activator and prolongs the anagen phase of hair follicles in the following manner: minoxidil (1) induces cell growth factors such as VEGF, HGF, IGF-1 and potentiates HGF and IGF-1 actions by the activation of uncoupled SUR on the plasma membrane of dermal papilla cells, (2) inhibits of TGF beta induced apoptosis of hair matrix cells by opening the Kir 6.0 channel pore coupled with SUR on the mitochondrial inner membrane, and (3) dilates hair follicle arteries and increases blood flow in dermal papilla by opening the Kir 6.0 channel pore coupled with SUR on the plasma membrane of vascular smooth muscle cells.