C. T. Musabayane

Effects of Opuntia megacantha on blood glucose and kidney function in streptozotocin diabetic rats

The purpose of the study was to investigate the effects of Opuntia megacantha leaf extracts on blood glucose concentrations and kidney function in normal and streptozotocin (STZ)-diabetic rats. STZ-diabetic and non-diabetic rats were orally administered extracts of O. megacantha leaves (20 mg/100 g body weight) daily for 5 weeks and respective control rats were administered normal saline (0.1 ml/100 mg body weight). Urine volume, urinary outputs of Na+, K+ and creatinine were monitored daily over the 5-week period. Plasma concentrations of Na+, K+, urea and creatinine and the glomerular filtration rate (GFR) as assessed by creatinine clearance were determined after 5 weeks. Plasma glucose concentrations in STZ-diabetic and non-diabetic rats were reduced by the administration of leaf extracts of O. megacantha. However, leaf extracts increased urinary Na+ output in STZ-diabetic and non-diabetic rats, concomitantly with a reduction in plasma concentration of the ion. O. megacantha leaf extracts significantly increased plasma creatinine and urea concentrations in non-diabetic and STZ-diabetic rats. Administration of the leaf extract was also associated with an increased GFR in STZ-diabetic rats (from 1.8 +/- 0.3 ml/min to 2.8 +/- 0.3 ml/min, n = 8) although the rate was unaltered in non-diabetic rats. The results suggest that leaf extracts of O. megacantha not only reduce blood glucose levels, but may be toxic to the kidney as shown by the elevation in plasma urea and creatinine concentrations and the reduction of plasma Na+ concentration.

Renal Effects of Plant-Derived Oleanolic Acid in Streptozotocin-Induced Diabetic Rats

Previous studies from our laboratories indicate that the anti-diabetic effects of Syzygium cordatum (Hochst.) [Myrtaceae] leaf extract in streptozotocin-induced diabetic rats may be attributed in part to mixtures of triterpenes, oleanolic acid (3ß-hydroxy-olea-12-en-28-oic acid, OA) and ursolic acid (3ß –hydroxyl-urs-12-en-28-oic acid, UA). For the bioactive compounds to have potential in diabetes management, they should alleviate or prevent complications of diabetes mellitus, kidney function, and cardiovascular disorders. This study was, therefore, designed to assess whether S. cordatum leaf derived OA influenced renal function evaluated by the ability to increase urinary Na+ outputs parameters and creatinine clearance (Ccr) of streptozotocin (STZ)-induced diabetic rats. Extraction and fractionation of S. cordatum powdered leaf ethyl acetate-solubles (EAS) yielded mixtures of OA/UA and methyl maslinate/methyl corosolate. Recrystallization of OA/UA mixture using ethanol afforded OA, the structure of which was confirmed by NMR spectroscopy (1H & 13C). Acute effects of OA on kidney function and mean arterial blood pressure (MAP) were investigated in anesthetized rats challenged with hypotonic saline after a 3.5-h equilibration for 4h of 1 h control, 1.5 h treatment, and 1.5 h recovery periods. OA was added to the infusate during the treatment period. Chronic effects of OA were studied in individually caged rats treated twice daily with OA (60 mg/kg, p.o.) for five weeks. By comparison with respective control animals administration, OA significantly increased Na+ excretion rates of non-diabetic and STZ-induced diabetic rats without affecting urine flow, K+ and Cl− rates. At the end of five weeks, OA treatment significantly (p < 0.05) increased Ccr in non-diabetic (2.88 ± 0.14 vs. 3.71 ± 0.30 ml/min) and STZ-diabetic rats (1.81 ± 0.32 vs. 3.07 ± 0.16 ml/min) with concomitant reduction of plasma creatinine concentration (n = 6 in all groups). OA also caused significant decreases in MAP in non-diabetic and STZ-induced diabetic rats. These findings suggest that OA may have beneficial effects on some processes associated with renal derangement of STZ-induced diabetic rats.

Sclerocarya birrea [(A. Rich.) Hochst.] [Anacardiaceae] stem-bark ethanolic extract (SBE) modulates blood glucose, glomerular filtration rate (GFR) and mean arterial blood pressure (MAP) of STZ-induced diabetic rats.

Studies in our laboratories suggest that Sclerocarya birrea stem-bark ethanolic extract (SBE) has hypoglycemic properties. Accordingly, we investigated the effects of SBE on major complications of diabetes mellitus; blood glucose, renal function and mean arterial blood pressure (MAP) in non-diabetic and STZ-induced diabetic rats. Oral glucose tolerance test responses to various SBE doses (60, 120 and 240 mg kg(-1)) were studied in fasted rats following glucose load (0.86 g kg(-1), p.o.). Rats treated with deionized water (3 ml kg(-1) p.o.), or standard hypoglycemic drugs (insulin, 100 microg kg(-1), s.c.; metformin, 500 mg kg(-1), p.o. or glibenclamide, 500 microg kg(-1), p.o) acted as untreated and treated positive controls, respectively. Blood was collected in non-diabetic rats after 45 min of SBE, metformin or glibenclamide for plasma insulin determination. Acute SBE effects on renal function and MAP were studied in anesthetized rats challenged with hypotonic saline after 3.5h equilibration for 4h of 1h control, 1.5h treatment and 1.5h recovery periods. SBE was added to the infusate during the treatment period. Chronic effects were monitored for 5 weeks in animals daily treated with SBE (120 mg kg(-1) p.o.) while hepatic glycogen concentration was measured at the end of the experimental period. SBE exhibited dose-dependent reduction in blood glucose concentration. SBE and metformin did not affect plasma insulin secretion in non-diabetic rats, while glibenclamide increased plasma insulin concentration. The hypoglycemic effect of SBE treatment was associated with increased hepatic glycogen synthesis. Acute SBE administration did not significantly alter kidney function, but chronic SBE treatment for decreased plasma urea and creatinine concentrations of STZ-diabetic rats with concomitant increase in GFR by comparison with control rats at the corresponding period (0.7+/-0.2 vs. 1.4+/-0.3 ml min(-1)). SBE treatment reduced blood pressure in all groups of animals. The observations suggest that SBE has reno- and cardio-protective effects in diabetes mellitus. The current results indicate the basis for SBE use as complementary remedy in diabetes.

Synergistic antihyperglycemic effects between plant-derived oleanolic acid and insulin in streptozotocin-induced diabetic rats

Studies from our laboratories indicate that Syzygium cordatum leaf extract contains triterpene mixtures [oleanolic acid (OA) and ursolic acid (UA)] with hypoglycemic properties. The aims of this study were to investigate the hypoglycemic effects of Syzygium aromaticum-derived OA and whether OA influenced the blood glucose lowering effects of insulin in streptozotocin (STZ)-induced diabetic rats. We envisaged that OA may provide a strategy with different mechanism of action for effective diabetic therapy because no single-marketed antidiabetic drug is capable of achieving long-lasting blood glucose control. The effects of various doses of OA and/or standard antidiabetic drugs on blood glucose were monitored in nondiabetic and STZ-induced diabetic rats given a glucose load after an 18-h fast. Rats treated with deionized water and standard antidiabetic drugs acted as untreated and treated positive controls, respectively. Blood glucose concentrations were measured at 15-min intervals for the first hour and hourly thereafter for 3 h. Blood glucose concentrations were also monitored in animals treated with OA and/or standard antidiabetic drugs for 5 weeks. OA like insulin decreased blood glucose concentrations in nondiabetic and STZ-induced diabetic rats. Combined OA and insulin treatment had even greater antihyperglycemic response, suggestive of a synergistic effect of the two. After 5 weeks, STZ-induced diabetic rats exhibited hyperglycemia and depleted hepatic and muscle glycogen concentrations. OA treatment lowered the blood glucose with concomitant restoration of glycogen concentrations to near normalcy. Our results suggest that OA may have a role in improving insulin sensitivity. These findings merit further research in this field.

Transdermal Delivery of Chloroquine by Amidated Pectin Hydrogel Matrix Patch in the Rat

The aim of the present study was to investigate the suitability of amidated pectin matrix patch for transdermal chloroquine delivery in an effort to mask the bitter taste when orally administered. Chloroquine has easily measurable outputs that are linked to increased renal Na+ excretion. We thus monitored urinary Na+ output in separate groups intravenously administered chloroquine or topically applied pectin hydrogel chloroquine matrix patch. Male groups of anesthetized Sprague-Dawley rats were placed on a continuous jugular infusion of 0.077 M NaCl at 150 µL min−1. After 3 h equilibration period, consecutive 20 min urine collections were made over the subsequent 4 h of 1 h control, 1 h 20 min treatment, and 1 h 40 min recovery periods for measurements of urine flow and Na+ and K+ excretion rates. The effects of intravenous chloroquine infusion or topical application of pectin hydrogel chloroquine matrix patch were examined in rats in which the drug was added to the infusate or patch applied onto the shaved area during the 1 h 20 min treatment period. The animals were switched back to the infusate alone for the final 1 h 40 min recovery period. Vehicle infused animals acted as controls. Trunk blood was collected after the treatment period from parallel groups for chloroquine measurements. The plasma chloroquine concentrations following iv chloroquine or application of pectin chloroquine hydrogel matrix patch were 9.3 ± 0.8 mg L−1 and 7.3 ± 1.1 mg L−1, respectively (n = 7 in both groups). Chloroquine infusion and pectin chloroquine patch significantly (p<0.01) increased Na+ excretion to peak values of 14.1 ± 0.9 µmol min−1, and 20.35 ± 1.0 µmol min−1, respectively by comparison with controls (9.1 ± 0.9 µmol min−1), at the corresponding period. The results suggest that the pectin chloroquine patch matrix preparation has potential applications for transdermal delivery of chloroquine and perhaps in the management of malaria.

Effects of Syzygium aromaticum-derived triterpenes on postprandial blood glucose in streptozotocin-induced diabetic rats following carbohydrate challenge.

Purpose Recent reports suggest that the hypoglycaemic effects of the triterpenes involve inhibition of glucose transport in the small intestine. Therefore, the effects of Syzygium spp-derived triterpenes oleanolic acid (OA) and maslinic acid (MA) were evaluated on carbohydrate hydrolyzing enzymes in STZ-induced diabetic rats and consequences on postprandial hyperglycaemia after carbohydrate loading. Methods We determined using Western blot analysis the expressions of α-amylase and α-glucosidase and glucose transporters SGLT1 and GLUT2 in the small intestine intestines isolated from diabetic rats treated with OA/MA for 5 weeks. In vitro assays were used to assess the inhibitory activities of OA and MA against α-amylase, α-glucosidase and sucrase. Results OA and MA ameliorated postprandial hyperglycemia in carbohydrate loaded diabetic rats as indicated by the significantly small glucose area under the curve (AUC) in treated diabetic animals compared with that in untreated diabetic rats. Western blotting showed that OA and MA treatment not only down-regulated the increase of SGLT1 and GLUT2 expressions in the small intestine of STZ-induced diabetic rats, but also inhibited small intestine α-amylase, sucrase and α-glucosidase activity. IC50 values of OA against α-amylase (3.60 ± 0.18 mmol/L), α-glucosidase (12.40 ± 0.11 mmol/L) and sucrase (11.50 ± 0.13 mmol/L) did not significantly differ from those of OA and acarbose. Conclusions The results of suggest that OA and MA may be used as potential supplements for treating postprandial hyperglycemia. Novelty of the Work The present observations indicate that besides improving glucose homeostasis in diabetes, OA and MA suppress postprandial hyperglycaemia mediated in part via inhibition of carbohydrate hydrolysis and reduction of glucose transporters in the gastrointestinal tract. Inhibition of α-glucosidase and α-amylase can significantly decrease the postprandial hyperglycaemia after a mixed carbohydrate diet and therefore can be an important strategy in the management of postprandial blood glucose levels in NIDDM patients.

The Effects of Syzygium aromaticum-Derived Oleanolic Acid on Glycogenic Enzymes in Streptozotocin-Induced Diabetic Rats

Studies indicate that the antihyperglycemic effects of Syzygium aromaticum-derived oleanolic acid (OA) are mediated in part through increased hepatic glycogen synthesis. Accordingly, this study assessed the influence of OA on the activity of glucokinase (GK) and hexokinase (HK) of skeletal muscle and liver tissues in streptozotocin (STZ)-induced diabetic rats. After 5 weeks of OA treatment, hepatic and gastrocnemius muscle glycogen concentrations and activities of GK and HK were measured spectrophotometrically in reactions where the oxidation of glucose-6-phosphate (G-6-PDH) formed was coupled to nicotinamide adenine dinucleotide phosphate (NADP+) reduction catalyzed by G-6-PDH dehydrogenase. Rats treated with deionized water or standard hypoglycemic drugs acted as untreated and treated positive controls, respectively. STZ-induced diabetic rats exhibited depleted glycogen levels and low activities of glycogenic enzymes in muscle and hepatic tissues. OA administration restored these biochemical alterations to near normalcy. The combination of OA and insulin did not significantly alter the activities of HK and GK of STZ-induced diabetic rats, suggesting that glycogen synthesis can also occur from precursors such as amino acids or fructose and lactate. The attenuation of the activities of glycogenic enzymes with concomitant increases of hepatic and muscle glycogen concentrations of STZ-induced diabetic rats provides a therapeutic strategy for diabetes treatment.

Effects of Hypoxis hemerocallidea (Fisch. & C.A. Mey.) (Hypoxidaceae) Corm (African Potato) Aqueous Extract on Renal Electrolyte and Fluid Handling in the Rat

Current biomedical evidence suggests that Hypoxis hemerocallidea (Fisch. & C.A. Mey.) [Hypoxidaceae] (African Potato [AP]) corm extract may be useful in the management of type 2 diabetes mellitus. However, more recent reports have also indicated that certain herbal extracts attenuate the deterioration of kidney function in diabetes mellitus. Accordingly, this study investigated the effects of short- (acute) and long-term (chronic) administration of H. hemerocallidea corm aqueous extract (APE) on renal fluid and electrolyte handling in male Wistar rats. Acute effects of APE were investigated in separate groups of anesthetized rats challenged with a continuous jugular infusion of 0.077 M NaCl at 9 mL · h− 1. After a 3.5-h equilibration period, consecutive 30-min urine collections were made over the subsequent 4 h of 1-h control, 1.5-h treatment, and 1.5-h recovery periods for measurements of urine flow, Na+, and K+ excretion rates. To establish the effects of acute APE, the extract was added to the infusate at doses of 90, 180, or 360 μg · h− 1 in separate groups of rats during the treatment period. For chronic studies, individually caged rats were administered twice with APE (30 mg · kg− 1 PO) every third consecutive day at 09h00 and 17h00 for 5 weeks. Control rats received distilled water (3 mL · kg− 1). Urine volume and total urinary outputs of creatinine, Na+, and K+ were determined from 24-h samples. Acute infusion of APE produced a dose-dependent, significant (p < 0.01) decrease in urine flow, K+, and Na+ excretion rates. Chronic APE treatment significantly reduced urinary Na+ output between weeks 2 and 5, without affecting either urine flow or K+ excretion rates. When compared with control animals, APE significantly reduced GFR (2.54 ± 0.09 mL · min− 1 vs. 1.52 ± 0.02 mL · min− 1) and increased plasma creatinine concentration (55 ± 3 µmol · L− 1 vs. 68 ± 6 µmol · L− 1). The results from this study suggest that the H. hemerocallidea corm aqueous extract may impair kidney function.

Transdermal delivery of insulin by amidated pectin hydrogel matrix patch in streptozotocin-induced diabetic rats: effects on some selected metabolic parameters

Purpose Studies in our laboratory are concerned with developing optional insulin delivery routes based on amidated pectin hydrogel matrix gel. We therefore investigated whether the application of pectin insulin (PI)-containing dermal patches of different insulin concentrations sustain controlled release of insulin into the bloodstream of streptozotocin (STZ)-induced diabetic rats with concomitant alleviation of diabetic symptoms in target tissues, most importantly, muscle and liver. Methods Oral glucose test (OGT) responses to PI dermal matrix patches (2.47, 3.99, 9.57, 16.80 µg/kg) prepared by dissolving pectin/insulin in deionised water and solidified with CaCl2 were monitored in diabetic rats given a glucose load after an 18-h fast. Short-term (5 weeks) metabolic effects were assessed in animals treated thrice daily with PI patches 8 hours apart. Animals treated with drug-free pectin and insulin (175 µg/kg, sc) acted as untreated and treated positive controls, respectively. Blood, muscle and liver samples were collected for measurements of selected biochemical parameters. Results After 5 weeks, untreated diabetic rats exhibited hyperglycaemia and depleted hepatic and muscle glycogen concentrations. Compared to untreated STZ-induced diabetic animals, OGT responses of diabetic rats transdermally applied PI patches exhibited lower blood glucose levels whilst short-term treatments restored hepatic and muscle glycogen concentrations. Plasma insulin concentrations of untreated diabetic rats were low compared with control non-diabetic rats. All PI treatments elevated plasma insulin concentrations of diabetic rats although the levels induced by high doses (9.57 and 16.80 µg/kg) were greater than those caused by low doses (2.47 and 3.99 µg/kg) but comparable to those in sc insulin treated animals. Conclusions The data suggest that the PI hydrogel matrix patch can deliver physiologically relevant amounts of pharmacologically active insulin. Novelty of the Work A new method to administer insulin into the bloodstream via a skin patch which could have potential future applications in diabetes management is reported.

Effects of Ficus thonningii (Blume) [Morarceae] Stem-Bark Ethanolic Extract on Blood Glucose, Cardiovascular and Kidney Functions of Rats, and on Kidney Cell Lines of the Proximal (LLC-PK1) and Distal Tubules (MDBK)

Previous observations indicate that Ficus thonningii (Blume) [Moraceae] stem-bark extracts may be useful in the control of diabetes mellitus. Accordingly, we investigated in some experimental animal paradigms the effects of F. thonningii stem-bark ethanolic extract (FTE) on renal and cardiovascular functions as complications of diabetes. Oral glucose tolerance tests were conducted in separate groups of non-diabetic and STZ-treated diabetic rats given glucose load (0.86 g.kg−1, p.o.) after 18-h fast, followed by various FTE doses (60, 120, and 240 mg.kg−1). Rats treated with deionized water (3 mL.kg−1 p.o.), or metformin (500 mg.kg−1 p.o.) acted as untreated and treated positive controls, respectively. Blood glucose was monitored at 15-min intervals for the first hour, and hourly thereafter for 3 h. Acute effects of FTE on kidney function and mean arterial blood pressure (MAP) were investigated in anaesthetized rats challenged with hypotonic saline after a 3.5-h equilibration for 4 h of 1 h control, 1.5 h treatment, and 1.5 h recovery periods. FTE was added to the infusate during the treatment period. Chronic effects of FTE were studied in individually caged rats treated daily with FTE (120 mg.kg−1, p.o.) for five weeks. Cytotoxicity of FTE was assessed by dye-reduction colorimetric (MTT) assay on MDBK and LLCPK1 kidney cell lines exposed for 24 h, 48 h, and 72 h to graded concentrations of the extract. Myocardial contractile performance was evaluated on rat isolated atrial muscle strips. FTE, like metformin, decreased blood glucose levels in non-diabetic and STZ-diabetic rats. Both acute and chronic FTE treatments did not affect renal function. In vitro studies demonstrated that FTE increased MDBK cell metabolic activity by an average of 15% (72 h), and LLCPK1 mirrored the controls. Acute intravenous infusion of FTE reduced the MAP from 119 ± 1 mmHg to 98 ± 4 mmHg. The MAP also was reduced throughout the five-week experimental study period. FTE also produced concentration-dependent, negative inotropic and chronotropic effects on rat isolated, electrically driven left-, and spontaneously beating right-, atrial muscle preparations. Our experimental findings suggest that FTE possesses reno- and cardio-protective effects in diabetes mellitus.