The effects of long-term treatment of streptozotocin-diabetic rats with an aldose reductase inhibitor

Mesenchymal stromal cell-derived exosomes improve mitochondrial health in pulmonary arterial hypertension

Secreted exosomes are bioactive particles that elicit profound responses in target cells. Using targeted metabolomics and global microarray analysis, we identified a role of exosomes in promoting mitochondrial function in the context of pulmonary arterial hypertension (PAH). Whereas chronic hypoxia results in a glycolytic shift in pulmonary artery smooth muscle cells (PASMCs), exosomes restore energy balance and improve O₂ consumption. These results were confirmed in a hypoxia-induced mouse model and a semaxanib/hypoxia rat model of PAH wherein exosomes improved the mitochondrial dysfunction associated with disease. Importantly, exosome exposure increased PASMC expression of pyruvate dehydrogenase (PDH) and glutamate dehydrogenase 1 (GLUD1), linking exosome treatment to the TCA cycle. Furthermore, we show that although prolonged hypoxia induced sirtuin 4 expression, an upstream inhibitor of both GLUD1 and PDH, exosomes reduced its expression. These data provide direct evidence of an exosome-mediated improvement in mitochondrial function and contribute new insights into the therapeutic potential of exosomes in PAH.

Postprandial plasma fructose level is associated with retinopathy in patients with type 2 diabetes

The aim of the present study was to investigate the association of fructose on microangiopathy in patients with diabetes. Postprandial plasma fructose concentrations and postprandial plasma glucose concentrations were simultaneously measured 3 times within a 24-hour period (2 hours after each meal) in 38 patients with type 2 diabetes that had been admitted to the hospital. The mean postprandial plasma fructose concentrations (MPPF) and the mean postprandial plasma glucose concentrations (MPPG) were calculated. Fructose was measured by gas chromatography-mass spectrometry (GCMS). Based solely on MPPF, we were able to divide the patients into three groups: the high MPPF (31.9 +/- 6.5 micromol/L) group (n = 12), the middle MPPF (21.2 +/- 1.8 micromol/L) group (n = 13), and the low MPPF (15.2 +/- 2.4 micromol/L) group (n = 13). Prevalence and degree of retinopathy and nephropathy were then evaluated in the 3 different groups. A significant correlation was observed in the prevalence of proliferative diabetic retinopathy (PDR) among the 3 MPPF groups (P =.024). The prevalence of PDR was higher in the high MPPF group (75.0%) than in the middle and low MPPF groups (23.1% and 38.5%, respectively). Although not significantly different statistically, the prevalence of all degrees of retinopathy showed a tendency to be higher in the high MPPF group (83.3%) than in the middle and low MPPF groups (46.2% and 46.2%, respectively) (P =.081). Nephropathy prevalence also showed a tendency to be higher in the high MPPF group (66.7%) than in the middle and low MPPF groups (38.5% and 30.8%, respectively), although the differences were not significant. The prevalence of clinical albuminuria was not significantly different among the 3 groups, but there was a tendency for it to be higher in the low MPPF group (30.8%) than in the high and middle MPPF groups (16.7% and 0%, respectively). No significant differences in glycemic indicators and mean duration of diabetes were observed among the 3 groups. The increased prevalence of retinopathy in the high MPPF group suggests that fructose is associated with retinopathy in patients with type 2 diabetes.

Increased fructose concentrations in blood and urine in patients with diabetes

OBJECTIVE

To investigate fructose metabolic changes in patients with diabetes.

RESEARCH DESIGN AND METHODS

Serum and urinary fructose concentrations were determined in healthy subjects (n = 23) and in nondiabetic (n = 23) and diabetic patients (n = 26). Fructose was measured using our newly developed method, and (13)C(6)-fructose was used as the internal standard. After adding sample to a fixed amount of internal standard, ion-exchange resins and high-performance liquid chromatography pretreatments were performed. Then, the amount of fructose in the sample was measured by gas chromatography-mass spectrometry.

RESULTS

Serum fructose concentrations in patients with diabetes (12.0 +/- 3.8 micromol/l) were significantly higher than those in healthy subjects (8.1 +/- 1.0 micromol/l, P < 0.001) and nondiabetic patients (7.7 +/- 1.6 micromol/l, P < 0.001), and daily urinary fructose excretion was significantly greater in patients with diabetes (127.8 +/- 106.7 micromol/day) than in nondiabetic patients (37.7 +/- 23.0 micromol/day, P < 0.001). In patients with diabetes (n = 20), serum fructose concentrations (8.6 +/- 1.8 micromol/l, P < 0.001) and daily urinary fructose excretion (63.4 +/- 63.8 micromol/day, P < 0.01) significantly decreased by week 2 after admission.

CONCLUSIONS

The present results differed from those of previous studies in that we found that the serum and urinary fructose concentrations decreased rapidly, concomitant with an improvement in glycemia. Therefore, hyperglycemia was associated with increased serum and urinary fructose concentrations in patients with diabetes.

Decreased skin blood flow early in the course of streptozotocin-induced diabetes mellitus in the rat

We have previously used laser Doppler technology to demonstrate that skin blood flow is reduced in Type 1 (insulin-dependent) diabetic patients. The possibility of using the skin as an extremely accessible indicator of diabetic microvascular disease is attractive. The streptozotocin diabetic rat is an appealing potential animal model. We performed measurements of skin blood flow in two rat species, nine Sprague Dawley (SD) rats and nine Wistar Kyoto (WKY) rats, observing early changes following the inception of diabetes. Four of the SD rats and five of the WKY rats were made diabetic, the rest serving as controls. There were no significant differences in skin blood flow between the two rat strains. As in man, there appear to be rat skin sites with primarily nutritive capillary supply and those with arteriovenous anastomotic predominance. The back and base of tail, both hair-covered areas, demonstrated low flow characteristics, consistent with nutritive perfusion. In contrast, the plantar surface of the paw behaved similarly to the finger or toe pulps in man, sites of arteriovenous perfusion, with high basal flow and a marked increment with thermal stimulation. In diabetic rats of both species, there was significantly lower flow at the back and base of tail than in non-diabetic animals. The differences were of the order of 30-40%. As a function of time, the decrease in blood flow at the base of tail parallelled the increase in glycohaemoglobin levels in the diabetic rats. In contrast, blood flow at the plantar surface of the paw was unchanged throughout the 3-month post-streptozotocin observation period.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in cardiac muscle fructose content in streptozotocin-induced diabetic rats

To evaluate the activation of the sorbitol pathway in cardiac muscle in diabetic rats, we measured sorbitol, fructose, and myo-inositol content in cardiac tissue obtained from control and streptozotocin-diabetic rats, with or without an 8-week insulin treatment, using gas chromatography-mass spectrometry (GC-MS). Cardiac fructose and sorbitol content in 10-week diabetic rats increased by 60-fold and 3.9-fold of those of control rats, respectively (P less than .001). In contrast, cardiac myo-inositol content in 10-week diabetic rats decreased to 56% (P less than .025) of the control value. The abnormalities in cardiac fructose, sorbitol, and myo-inositol content were completely normalized by the 8-week insulin treatment, which was initiated 2 weeks after the induction of diabetes. There was no difference in cardiac aldose reductase activity between control and diabetic rats. However, cardiac sorbitol dehydrogenase activity in diabetic rats was 151% (P less than .005) higher than that of control rats, although hepatic sorbitol dehydrogenase activity was not different between the two groups. These results indicate that the sorbitol pathway is significantly activated in cardiac tissue obtained from streptozotocin-induced diabetic rats, which results in the marked cardiac accumulation of fructose.

Aldose reductase inhibitors and diabetic complications

Aldose reductase inhibitors impede flux of glucose through the sorbitol pathway in diabetes mellitus. They therefore reduce the accumulation of the pathway metabolites, sorbitol and fructose, reduce the impact of the flux on the cofactors used by the pathway and reduce other derived phenomena, such as osmotic stress and myo-inositol depletion. As drugs, their targets are the chronic complications of diabetes--neuropathy, retinopathy, nephropathy and vasculopathy. In experimental models there is proof of activity against biochemical, functional and structural defects in all of the involved tissues, but we await full clinical verification of this potential.

Evaluation of the effect of aldose reductase inhibition on increased basement membrane collagen fluorescence in diabetic rats

1. It has been proposed that increased fructose contributes to the formation of fluorescent pigments in diabetic tissues. 2. Since the aldose reductase inhibitor sorbinil lowers glomerular fructose concentrations, we examined the effect of sorbinil on the formation of advanced glycation end products in glomerular basement membrane of streptozotocin diabetic rats. 3. Treatment with sorbinil for 30 days after induction of diabetes did not influence the increased fluorescence observed in collagen from glomerular basement membrane of untreated diabetic rats. 4. The results suggest that nonenzymatic glycation by fructose is not a major contributor to the formation of fluorescent advanced glycation end products in basement membrane in experimental diabetes.

Polyol pathway in tissues of spontaneously diabetic Chinese hamsters (Cricetulus griseus) and the effect of an aldose reductase inhibitor, ONO-2235

1. Sorbitol and fructose levels were significantly elevated in the lens, the sciatic nerve, the retina and the kidney of diabetic Chinese hamsters and inositol level was significantly decreased in the lens and sciatic nerve of diabetics. 2. The activity of an aldose reductase in the kidney was not different between normal and diabetic Chinese hamsters. 3. An aldose reductase inhibitor (ONO-2235) had no effect in sorbitol, fructose and inositol contents of all these tissues from diabetic Chinese hamsters. 4. These results suggest that diabetic Chinese hamsters produce polyol accumulation in tissues but that there is a clear species-specific difference to inhibition of aldose reductase.

Effects of long-term diabetes and galactosaemia upon lens and retinal mRNA levels in the rat

The levels of mRNAs encoding the alpha 1 chain of collagen IV and the B1 chain of laminin were assayed in the lenses and retinas of long-term (28-week) diabetic and galactosaemic rats in order to gain some insight into the effects on basement membrane (BM) synthesis in these tissues. mRNAs coding for beta-actin, glucose transporter protein and the alpha 2 catalytic subunit of Na+,K(+)-ATPase were also assayed to determine whether any effects on BM-coding mRNA levels were specific. Long-term diabetes had no significant effect on the levels of alpha 1 (IV) collagen mRNA but caused a significant reduction in the laminin B1 message in the lens. In the same samples, the level of the glucose transporter protein mRNA was found to be elevated significantly in the diabetic tissue, whereas the mRNAsen coding beta-actin and alpha 2 Na+,K(+)-ATPase were unaffected in comparison with age-matched controls. Long-term galactosaemia resulted in significant increases in the levels of all mRNAs assayed when expressed per micrograms total RNA used for each analysis. However, this effect appeared to be due to a specific loss of ribosomal RNA from these severely cataractous lenses. When related to the beta-actin mRNA internal control, the levels of mRNA in the galactosaemic lenses were very similar to that found in the diabetics. Laminin B1 mRNA levels were decreased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration of an aldose reductase inhibitor induces a decrease of collagen fluorescence in diabetic rats

As a consequence of an increased flux through the sorbitol pathway fructose levels rise in various tissues in diabetes. Also, in vitro nonenzymatic fructosylation of protein induces the generation of fluorescence at a rate 10 times greater than glucosylation. The administration of sorbinil, an aldose reductase inhibitor known to lower tissue fructose concentration, to experimental diabetic rats led to a decrease in the fluorescence related to advanced Maillard products in their skin collagen. This effect is consistent with the in vivo occurrence of nonenzymatic fructosylation of collagen. A potential pathogenetic role for this posttranslational modification in diabetic complications should be considered.

Pathogenetic heterogeneity in retinal capillary basement membrane thickening in the diabetic BB-rat

In the present study, we compared the effects of good blood glucose control and that of aldose reductase inhibitor (Statil) treatment on diabetic retinal capillary basement membrane thickening in the diabetic BB-rat. Aggressive insulin treatment maintaining euglycaemia for 4 months prevented the characteristic basement membrane thickening in both the superficial and deep capillary beds of the diabetic retina. Statil treatment of hyperglycaemic rats for the same length of time prevented basement membrane thickening in the deep capillary bed but not in the superficial capillaries.

The effects of sorbinil on peripheral nerve conduction velocity, polyol concentrations and morphology in the streptozotocin-diabetic rat

This study examined the effects of an aldose reductase inhibitor, Sorbinil, on neuropathy over a 6-month period in streptozotocin-diabetic rats. Sorbinil treatment prevented the 10-fold increase in nerve sorbitol found with diabetes. It produced a 60% improvement in tibial nerve motor conduction velocity after 6 months. Morphometric profiles of nerves were also normalized. Axon area was reduced by 14% in untreated diabetic rats compared to age-matched controls, whereas Sorbinil-treated animals showed normal age-related axon growth. Myelin area was increased by 28% in untreated diabetic animals, but was the same as age-matched controls with Sorbinil treatment. Nerve myo-inositol levels were reduced by 45% after three months of untreated diabetes, but were normal after six months. Sorbinil treatment tended to restore myo-inositol levels toward normal over the shorter time period. It was concluded that axon growth retardation is the most likely cause of the conduction deficit seen in long-term experimental diabetes.