Effects of torbafylline, pentoxifylline and buflomedil on vascularisation and fibre type of rat skeletal muscles subjected to limited blood supply

Effect of cilostazol and pentoxifylline on gait biomechanics in rats with ischemic left hindlimb

OBJECTIVE

The purpose of this study was to determine the impact of pharmacologic treatment with cilostazol and pentoxifylline on gait biomechanics of ischemic rat hindlimbs compared with nonischemic controls.

METHODS

An experimental study was designed using 30 Wistar rats divided into five groups (n = 6): control (C); ischemia (I) - animals submitted to left common iliac artery interruption without pharmacologic treatment; pentoxifylline (Pen) - rats submitted to procedure and treated with pentoxifylline 3 mg/kg twice a day for 6 weeks; cilostazol (Cil) - animals submitted to procedure and treated with cilostazol 30 mg/kg twice a day for 6 weeks; and sham (S) - animals submitted to procedure without artery interruption. Gait analysis was performed using a computed treadmill. Time, number, and duration of each hindlimb contact were obtained. The total number of contacts (TNC) and the total duration of contacts (TDC) were compared between left and right hindlimb and among groups. Left hindlimb ischemic incapacitation index (LHII) was defined by the formula: LHII = (1-TNCleft x TDCleft / TNCright x TDCright) x 100.

RESULTS

Left hindlimb TNC values were twofold lower in I, Pen, and Cil groups than in C and S groups (P < .01). In I, Pen, and Cil groups, TNC values for the left hindlimb were half of the right hindlimb ones (P < .01). Left hindlimb TDC values were lower in I and Pen groups than the other groups (P < .01). Cil group presented twofold increased values, not different from C and S groups (P = 0.16). Right hindlimb TNC values were greater for I group (P < .01). LHII was around zero in C and S groups and 82 in both I and Pen groups (P < .01). Cil group presented a LHII of 42; higher than C and S groups, but lower than I and Pen groups (P < .01).

CONCLUSIONS

Cilostazol at a dose of 30 mg/kg twice a day promoted improvement in gait performance in rats submitted to chronic hindlimb ischemia. Pentoxifylline at a dose of 3 mg/kg twice a day did not show this effect.

Buflomedil and pentoxifylline in the viability of dorsal cutaneous flaps of rats treated with nicotine

BACKGROUND

Nicotine reduces skin-flap survival. Pharmacologic therapy may represent an alternative treatment strategy to counteract nicotine effects in the flap surgery setting. In this study, we have compared the isolated and associated actions of the vasoactive drugs buflomedil and pentoxifylline in the viability of dorsal cutaneous flaps of rats treated with subcutaneous doses of nicotine.

METHODS

The survival of modified McFarlane skin flaps was assessed on post-operative day 7. Nicotine group received 4 mg/kg nicotine during 40 days pre-operatively and 7 days post-operatively. Nicotine+buflomedil group received nicotine and 6 mg/kg buflomedil 24 h pre-operatively and 7 days post-operatively. Nicotine+pentoxifylline group received nicotine and 20 mg/kg pentoxifylline in 15 pre-operatively and 7 post-operatively days. Nicotine+buflomedil+ pentoxifylline group received nicotine and both drugs administered as above. Control group received daily 1 ml normal saline during 40 days pre-operatively and 7 days post-operatively. Using image analysis, five different flap areas were quantified: Total, preserved, necrotic, ischaemic and viability. Viability areas comprised the sum of ischaemic and preserved areas.

RESULTS

Nicotine treated animals had lower percentage of viability areas (60.7% +/- 6.8) than the control group (73.7% +/- 9.5), p=0.016. The percentage of viability areas in the buflomedil (76.4% +/- 11.4), pentoxifylline (74.2% +/- 15.6) and buflomedil+ pentoxifylline (74.0% +/- 9.7) groups were larger than the nicotine group (p=0.002, p=0.011 and p=0.012, respectively). There were no significant differences in the viability areas when drugs were used isolated or in association. We further demonstrated that the increase in the viability area of the buflomedil and pentoxifylline groups (isolated or in association) was due to increase in ischaemic areas.

CONCLUSIONS

Both drugs equally increased flap survival in nicotine treated animals. Viability areas increased due to larger ischaemic areas, probably as a reflex of the action of these drugs in sites of partial circulatory deficit.

Chronic Transcutaneous Electrical Stimulation of Calf Muscles Improves Functional Capacity without Inducing Systemic Inflammation in Claudicants

OBJECTIVES

To assess whether electrical stimulation of ischaemic calf muscles in claudicants causes a systemic inflammatory response and to evaluate effects of its chronic application on muscle function and walking ability.

DESIGN

Prospective randomised controlled trial of calf muscle stimulation.

MATERIALS AND METHODS

Stable claudicants were randomised to receive either active chronic low frequency (6 Hz) motor stimulation (n=15) or, as a control treatment, submotor transcutaneous electrical nerve (TENS) stimulation (n=15) of calf muscles in one leg, 3 x 20 min per day for four weeks. Leucocyte activation was quantified by changes in cell morphology, vascular permeability by urinary albumin:creatinine ratio (ACR), calf muscle function by isometric twitch contractions and walking ability by treadmill performance pre- and post-intervention.

RESULTS

Acute active muscle stimulation activated leucocytes less (28% increase) than a standard treadmill test (81% increase) and did not increase ACR. Chronic calf muscle stimulation significantly increased pain-free walking distance by 35 m (95% CI 17, 52, P<0.001) and maximum walking distance by 39 m (95% CI 7, 70, P<0.05) while control treatment had no effect. Active stimulation prevented fatigue of calf muscles during isometric electrically evoked contractions by abolishing the slowing of relaxation that was responsible for loss of force.

CONCLUSIONS

Chronic electrical muscle stimulation is an effective treatment for alleviating intermittent claudication which, by targeted activation of a small muscle mass, does not engender a significant systemic inflammatory response.

Therapeutic potentials of pentoxifylline for treatment of cardiovascular diseases

BACKGROUND

Cardiovascular diseases are life-threatening conditions and, thus, have received a great deal of attention over the years. Several mechanisms, including hemorheology changes and inflammatory effects, are considered to be involved in the pathogenesis of these diseases. Because cardiovascular dysfunction is also known to worsen hemorheology changes and influence vital symptoms, it has become critical to formulate effective therapeutic strategies to combat the deleterious effects of cardiovascular diseases. Although a wide variety of drugs have been developed for the treatment of cardiovascular diseases, the effectiveness of any agent for therapy of a given disease cannot be indicated with certainty.

OBJECTIVES AND OBSERVATIONS

Pentoxifylline (PTXF), a phosphodiesterase inhibitor, has been investigated for close to two decades because of its primary pharmacological actions on hemorheology and other anti-inflammatory effects. Several studies have been conducted to investigate the effects and mechanisms of PTXF in ischemic injury, peripheral vascular disease and heart failure. The present article is intended to emphasize the therapeutic potentials of PTXF in different types of cardiovascular diseases, focusing on the mechanisms of its pharmacological actions.

Muscle ischaemia in rats may be relieved by overload-induced angiogenesis

Alleviation of muscle ischaemia by improving capillary supply has proved difficult, possibly reflecting the inability to substantially increase blood flow. We reasoned that muscle overload, which induces angiogenesis in the absence of altered blood flow, may be an alternative to drug therapy. Male Wistar rats underwent unilateral ligation of the common iliac artery, with or without ipsilateral extirpation of the tibialis anterior muscle. Six weeks later ischaemic (I) extensor digitorum longus (EDL) had a 10% (P < 0.05) decrease in relative muscle mass, while overloaded muscles (O) had undergone hypertrophy of 39% and 52% relative to contralateral (CL) and control (C) muscle masses, respectively (P < 0.01). Muscle atrophy was prevented by the combination of overload and ischaemia (O/I), with hypertrophy of 24% (vs. CL) and 35% (vs. C), respectively (P < 0.01). Changes in muscle fibre cross-sectional area paralleled the changes in muscle mass, with means of 1898 +/- 59, 1531 +/- 90, 2253 +/- 155 and 2292 +/- 80 mm2 for C, I, O and O/I, respectively (P < 0.01 vs. C and I). Capillary to fibre ratio (C:F) was significantly increased in overloaded (2.58 +/- 0.09) compared to contralateral (1.78 +/- 0.04), control (1.61 +/- 0.05) and ischaemic (1.73 +/- 0.06) muscles (P < 0.001). A similar increase in C:F was seen in overloaded plus ischaemic muscle (2.59 +/- 0.07) compared to contralateral (1.40 +/- 0.01) and control or ischaemic values (P < 0.01). In both O and O/I muscle groups, C:F and capillary density (CD) increased most in the region of EDL where fibre size was largest, while hypertrophy of fibres was least in the same region for both groups. These data suggest that the microvascular deficit evident in chronic muscle ischaemia may be alleviated by angiogenesis that is induced by mechanical stimuli via chronic muscle overload.

Structural adaptation to ischemia in skeletal muscle: effects of blockers of the renin-angiotensin system

OBJECTIVE

To investigate the effects of long-term treatment with blockers of the renin-angiotensin system on capillarization and growth of fibers in ischemic hind-limb muscles and in muscles under normal growth conditions.

METHODS

Ischemia was induced by partial ligation of the left common iliac artery.

RESULTS

Ischemia resulted in a significant increase in capillary and fiber density in the soleus muscle, a significant decrease in mean fiber size and a decrease in muscle cross-sectional area after 4 weeks compared with the contralateral nonischemic muscle. Ischemia also significantly decreased the muscle: body weight ratio of the left soleus muscle. We observed no significant effect on total number of capillaries and capillary: fiber ratio, suggesting that ischemia did not result in an increase in capillarization in this muscle. Treatments with subhypotensive and with hypotensive doses of the angiotensin converting enzyme (ACE) inhibitor benazeprilat, the angiotensin (Ang) II AT1 antagonist valsartan, or the Ang II AT2 antagonist PD 123 319 for 4 weeks did not influence any of the above-described changes in the normal and ischemic muscles and treatment effects were also independent of the degree of reduction of blood pressure.

CONCLUSION

Treatments with an ACE inhibitor and with Ang II receptor antagonists in dose ranges that moderately lower blood pressure do not influence vessel density and any of the other structural adaptations after hind-limb ischemia. Administrations of ACE inhibitors and Ang II AT1 antagonists may therefore be adequate and beneficial therapies under ischemic conditions, such as in the treatment of hypertension complicated by intermittent claudication, for which treatment must not increase ischemia.

Endothelium as a therapeutical target in peripheral occlusive arterial diseases: consideration for pharmacological interventions

The aim of this review is to consider the role of endothelium in the establishment of injury induced by ischaemia and reperfusion with particular emphasis on the vascular beds of the legs. We review the main abnormalities found in the macro- and microcirculation in these conditions and discuss the various theories put forward to explain the mechanism by which endothelial injury is induced. Endothelial cells play a key role in maintaining patent and functional capillaries. When blood vessels are damaged they become unresponsive to vasodilatory stimuli and intraluminal thrombosis may occur. The relative contribution of platelets and leukocytes in the formation of final ischaemic damage is widely discussed. Furthermore, the role of reperfusion in causing damage to post-ischaemic vascular beds is considered as well. The degree to which post-ischaemic injury is reversible might define the opportunity for therapeutic interventions.

Gait analysis in the rat as a model for the study of peripheral vascular disease

A number of problems are associated with investigation of the pathophysiology of peripheral vascular disease (PVD) in humans and unilateral ligation of the common iliac artery in the rat has been extensively used as an experimental model of PVD. However, techniques so far applied to monitor the effects of PVD on muscular function are invasive and difficult to relate to natural locomotion. The present study aimed to investigate gait during spontaneous, unforced locomotion in the animal model. No differences were observed between control and experimental rats in velocity or stride lengths. Although stride time was unchanged, its internal balance was disturbed with reduced stance, prolonged swing, for the ligated limb (LL) relative to the nonligated limb (NLL). Gait symmetry was also affected with NLL strike occurring earlier during LL stance. Analysis of footfall patterns showed a reduction of stance area and pressures exerted via LL relative to NLL. It is concluded that gait and footfall analysis could be useful for assessing limb function under natural exercise conditions.

Phosphodiesterase inhibitory profile of some related xanthine derivatives pharmacologically active on the peripheral microcirculation

The cyclic nucleotide phosphodiesterase (PDE) inhibitory profile of four related xanthine derivatives: pentoxifylline (BL 191), propentofylline (HWA 285), torbafylline (HWA 448) and albifylline (HWA 138), pharmacologically active on the peripheral and/or cerebral microcirculation was established using the four main PDE isoforms present in rat heart cytosol. HPLC on a Mono Q ion-exchange column resolved four separate cyclic nucleotide PDE activities: a calmodulin-activated fraction (PDE I), a cGMP-stimulated fraction (PDE II), a cAMP-specific rolipram-sensitive fraction (PDE IV) and a cGMP-inhibited fraction (PDE III). Among the four compounds studies, only torbafylline and pentoxifylline inhibited more efficiently the calcium plus calmodulin-stimulated than the basal activity of PDE I. The four xanthine derivatives inhibited more potently the cGMP-stimulated than the basal activity of the cGMP-stimulatable PDE II, propentofylline being the most inhibitory (IC50: 20 microM). Except for propentofylline, which exhibited a marked selectivity toward the rolipram-sensitive PDE versus the cGMP-inhibited PDE III, the other xanthines modestly (IC50 in the 10(-4) M range) inhibited both cAMP-specific isoforms with similar potency. Propentofylline proved to be the best inhibitor whatever the considered isoform whereas torbafylline exhibited the weakest inhibitory potency with, however, some selectivity for PDE I.

Increased capillary density due to atrophy of ischaemic soleus muscle of the rat

This investigation was undertaken to determine whether a severe limitation of blood supply by external iliac artery ligation can change the number and density of capillaries in rat soleus muscle. The external iliac artery in one hindlimb was ligated for 2, 7 or 28 days, and the other, sham-operated, hindlimb was used as a control. Muscle blood flow in the ischaemic soleus muscle at 2, 7 and 28 days after external iliac artery ligation was significantly decreased compared with the control. The muscle fibre area and the ratio of the fibre area to body mass in the ischaemic soleus muscle at 28 days after the external iliac artery ligation were significantly reduced in the ischaemic soleus muscle, but no change in the number of capillaries per fibre was observed. Capillary density per millimetres squared at 28 days and the ratios of the number of capillaries around type I fibres to the fibre area at 7 and 28 days were significantly increased in the ischaemic soleus muscle (P < 0.05). These results suggested that long-term severe limitation of blood flow in the soleus muscle by ligation of the external iliac artery could have induced the increase in capillary density, as a result of atrophy of muscle fibres rather than capillary growth.

Antihypertensive therapy and adaptive mechanisms in peripheral ischemia

In the present experiments the effect of long-term peripheral ischemia on the capillary of two hind limb skeletal muscles was investigated in spontaneously hypertensive rats. Furthermore, the effect of antihypertensive therapy on changes in capillarity and on the previously observed hyperreactivity of the ischemic vascular bed to vasoconstrictors was investigated in perfused hind limbs of rats after long-term treatment with the angiotensin I converting enzyme inhibitors captopril (0.5 mg/kg.h) or zabiciprilate (0.025 mg/kg.h), the angiotensin II type 1 receptor antagonist losartan (0.625 mg/kg.h), or the calcium antagonist felodipine (0.042 or 0.42 mg/kg.h). Skeletal muscle ischemia in the left hind limb was induced by partial ligation of the left common iliac artery. Long-term (4 weeks) ischemia increased significantly the capillary-to-fiber ratio in the soleus muscle, composed predominantly of type I fibers in spontaneously hypertensive rats, of the ischemic hind limb, whereas capillarity in the contralateral muscle was not affected. Furthermore, capillarity in the gastrocnemius muscle (type II muscle fiber part) of both the ischemic and contralateral hind limb did not change. Long-term treatment with the angiotensin I converting enzyme inhibitors during ischemia abolished the increase in the capillary-to-fiber ratio in the soleus muscle, whereas a comparable antihypertensive dose of felodipine had no effect. Greater blood pressure reductions by both losartan and felodipine prevented increases in capillarization in skeletal muscle ischemia. With respect to vascular hyperreactivity during ischemia, only treatment with losartan normalized reactivity of the ischemic vascular bed to vasoconstrictors.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional capillary perfusion in muscles with limited blood supply: effects of torbafylline

Severe limitation of blood supply mainly affects the oxidative regions of skeletal muscles. In mammals, they are located medially and are thus not accessible to direct observation. We therefore investigated capillary perfusion in rat tibialis anterior, which has a predominantly glycolytic cortex and oxidative core, using timed intraarterial injection of the fluorochrome thioflavine S conjugated with serum albumin. Muscles with intact blood supply were compared with those in which the blood supply had been limited for 5 weeks by unilateral ligation of the common iliac artery. The effect of a new xanthine derivative, torbafylline (1% solution, 12.5 mg/kg, in two daily doses by gavage, 7 days/week), was also studied. The capillary/fibre ratio was estimated for perfused capillaries (those filled with fluorochrome within 7.5 s after injection; Cp) and all capillaries (those subsequently stained for alkaline phosphatase; Ct), from micrographs of cryostat sections. Regional differentiation in relative capillary perfusion was evident in all muscles samples. Cp:Ct was 0.406 +/- 0.086 (mean +/- 95% CI) in the glycolytic cortex of the contralateral normal muscle, and 0.255 +/- 0.071 in the oxidative core. Muscles with limited blood supply had a significantly lower proportion of perfused capillaries, 0.119 +/- 0.056 in glycolytic and 0.034 +/- 0.038 in oxidative regions. Torbafylline treatment nearly doubled perfusion in the glycolytic regions (Cp:Ct = 0.216 +/- 0.137) and nearly quadrupled it in oxidative (Cp:Ct = 0.121 +/- 0.151) regions of ischaemic muscles. It also improved perfusion in the contralateral muscles (Cp:Ct = 0.705 +/- 0.085 in the glycolytic cortex and 0.583 +/- 0.230 in the oxidative core).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of torbafylline on enzyme activities in fast and slow muscles with limited blood supply

1. Activities of a glycolytic enzyme--lactate dehydrogenase, LDH, and two oxidative enzymes--citrate synthase (CS), a marker for TCA cycle entry, and 3-hydroxyacyl-CoA dehydrogenase (HAD), which indicates the capacity for beta-oxidation of endogenous lipids, were measured in fast (tibialis anterior, TA, and extensor digitorum longus, EDL) and slow (soleus, SOL) muscles of Sprague-Dawley rats with intact and limited blood supply, and following treatment with the xanthine derivative torbafylline (Hoechst, Werk Albert, Wiesbaden). 2. Limitation of blood supply by unilateral ligation of the common iliac artery increased activity of LDH in fast muscles, and activity of CS and HAD in soleus. 3. Torbafylline treatment caused an increased LDH activity in intact fast muscles and decreased it in soleus, although the relative capacity for anaerobic and aerobic metabolism (indicated by the ratio of LDH and CS activities) remained unchanged in all cases. 4. Whilst having little effect on oxidative enzyme activity of fast muscles, torbafylline decreased the activity of CS but increased activity of HAD in soleus, suggesting a greater reliance on lipid metabolism. 5. The effect of arterial ligation on enzyme activity was ameliorated by treatment with torbafylline, possibly due to its effect on the microcirculation.