Effect of torbafylline on muscle blood flow, performance, and capillary supply in ischemic muscles subjected to varying levels of activity.

Torbafylline, a novel xanthine derivative, was given to rats by gavage (2 x 25 mg.kg-1.day-1, morning and evening) to study its effect upon fast muscles (tibialis anterior and extensor digitorum longus) made ischemic by unilateral ligation of the common iliac artery and subjected to two types of activity imposed by chronic electrical stimulation at 10 Hz: (i) strenuous, 6 h.day-1 as 3 x 2 h with 90- to 120-min intervals or (ii) mild, 105 min.day-1 as 7 x 10-15 min with 90- or 85-min intervals for 12-14 days. Some of the deleterious effects on ischemic muscles of strenuous activity (reduced blood flow during contractions, less resistance to fatigue) were remedied by torbafylline treatment, and values normalized. Most notably, torbafylline significantly reduced the degree of capillary endothelial cell swelling. In addition, the degree of atrophy was reduced and fatigue resistance improved in muscles contralateral to ischemic, which had been impaired with the strenuous regime. Torbafylline treatment had little further effect on ischemic muscles subjected to mild stimulation, which on its own improved functional hyperemia, resistance to fatigue, and the capillaries per fibre ratio in tibialis anterior, although it did significantly increase the capillary per fibre ratio in extensor digitorum longus. These data indicate a possible role for torbafylline as an adjunct to exercise therapy for chronic muscle ischemia.

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.

Correlation of function and energy metabolism in rat ischemic skeletal muscle by 31P-NMR spectroscopy: effects of torbafylline.

The aim of this study was to correlate function of rat ischemic skeletal muscle directly with energy metabolism, to investigate the effects of torbafylline, a novel xanthine derivative potentially useful for the treatment of peripheral vascular occlusive disease and other ailments of skeletal muscle, and to get insight into its mechanism of action. Phosphocreatine (PCr), inorganic phosphate (Pi) and pH were estimated at rest, during induced contractions and during the recovery phase after cessation of electrical stimulation in rat hind limb muscles with two weeks unilateral chronic ligation of the femoral artery. Concomitantly, contraction force was measured in terms of tension developed during the stimulation interval. The effects of torbafylline [7-ethoxymethyl-1-(5-hydroxy-5-methylhexyl)3-methylxanthine] on the above parameters were studied after chronic oral gavage (25 mg/kg body weight per day); treatment started the day after surgery and the last drug application was performed the day of the final experiments. Control animals received physiological saline under the same conditions. During rest no major differences could be detected either in PCr and Pi levels or in pH between the different muscles, ischemic or not and treated or not. During compelled contractions, PCr and pH decreased and Pi increased in all muscles. Differences between muscles and treatments emerged as the PCr drop was more pronounced in ischemic saline treated muscles and the Pi increase in drug treated muscles (normal and ischemic) were clearly less marked than in saline treated ones. Contraction force decreased rapidly during the 12 min electrical direct stimulation and fatigability increased from 67% in normal muscle to 88% in ischemic muscle. Drug treatment induced strikingly less fatigability as it was 44.5% in normal and only 62% in ischemic muscle. However, most marked differences in metabolite levels and pH were measured during the recovery period. As an indication of disturbed energy balance, the recovery of PCr, Pi and pH was seriously hampered in ischemic saline treated muscles; especially pH being still significantly decreased during the entire chosen recovery period of 15 min. Torbafylline not only restored function, but also helped the muscle recover faster and better from exhaustion, as all the parameters returned gradually to normal levels.

Effects of torbafylline on muscle atrophy: prevention and recovery.

The effects of torbafylline on the prevention of and the recovery from 5 weeks of hindlimb suspension induced atrophy were analyzed in rat soleus and extensor digitorum longus muscles. Muscle alterations were investigated by determining a suite of electrophysiological, histochemical, and muscle ultrastructural characteristics. Administration of torbafylline during the suspension period was ineffective in preventing any of the observed muscle atrophic changes. Application of torbafylline during the recovery period resulted in a faster recovery of some soleus muscle structural and functional properties. Mitochondrial volume densities and capillary to fiber ratios returned towards baseline values earlier in the recovery process with torbafylline. Furthermore, the drug significantly improved soleus muscle fatigue resistance 4 weeks after cessation of hindlimb suspension.

Skeletal muscle microcirculation: the effects of limited blood supply and treatment with torbafylline.

The effects of one and two week arterial occlusion on the microcirculation of fast glycolytic skeletal muscle (rat tibialis anterior) were assessed by direct observation. Ligation of the right common iliac artery resulted in a greater proportion of the capillary population exhibiting intermittent flow, and reduction of capillary diameters. Terminal arterioles showed a lack of responsiveness to acute contractions of the muscle, while those in control muscles dilated. Acute infusion of torbafylline reduced the heterogeneity of flow by reducing the population of capillaries with intermittent flow and the time spent stationary by red cells. It also improved the pO2 at the muscle surface. Chronic oral administration of torbafylline for one week, started one week post-ligation, resulted in a similar response of the arterioles to muscle contractions as in control muscles and marginally improved the heterogeneity of flow.

The effects of torbafylline on blood flow, pO2 and function of rat ischaemic skeletal muscle.

Blood flow at rest and during contractions (measured with labelled microspheres), red cell flux (assessed by laser-Doppler flowmetry), surface pO2, lactate accumulation and release, the development of fatigue during acute muscle contractions, and performance in chronic experiments (running wheel) were estimated in rat hind limb muscles during unilateral acute occlusion or chronic ligation of the femoral artery. The effects of torbafylline (7-ethoxymethyl-1-(5-hydroxy-5-methylhexyl)3-methylxanthine) on the above-mentioned parameters were studied after acute i.v. infusion or chronic oral gavage. Torbafylline significantly ameliorated the decreased skeletal muscle blood flow, red cell flux and surface pO2 after acute occlusion of the femoral artery, with more pronounced effects on the microcirculatory parameters, the laser-Doppler flux and pO2. Chronic ligation of the femoral artery and consequent stimulation for 45 min induced increased fatigue (fatigue index in control muscles: 70%, in ligated muscles: 78%). Three weeks oral treatment with torbafylline (25 mg/kg per day) decreased fatigue to 68%. The blood flow in ligated muscles increased to a much smaller extent than in control muscles, and this smaller increase was attenuated by torbafylline. A chronic decrease in the blood supply resulted in a significant shortening of the running time. This decrease in running time was reversed by chronic treatment with torbafylline (25 mg/kg p.o. 2 times-day for 2 weeks). This improved performance may be explained by a decreased accumulation of lactate in muscles with a limited blood supply due to an effect of torbafylline to increase the release of lactate from ischaemic muscles.