ABSTRACT

Carbonic anhydrase (CA) is an ubiquitous enzyme catalyzing the reversible hydration of CO2 to HCO3- and H+. CA plays a crucial role in CO2 transport, acid-base balance, and in linking intracellular acidosis to O2 unloading from hemoglobin and also facilitates lactate shuttling across the monocarboxylate transporters (MCT). The study was aimed at investigating the influence of carbonic anhydrase on blood glucose concentration in Streptozotocin (STZ) induced type 1 diabetic rats, and to verify the potential antidiabetic activity of the leaves of C. farinosa Forssk. Carbonic anhydrase activity was determined by measuring the release of p-nitrophenol from p-nitrophenyl acetate. Glycated hemoglobin (HbA1c) was determined by ion exchange method. Glucose was determined based on glucose oxidase/ mediator reaction. Blood lactate was determined by lactate oxidase reaction. Superoxide dismutase (SOD) activity was determined by reacting with O2- substrate generated indirectly in the oxidation of epinephrine at alkaline pH.In the early phase of diabetes it was observed that carbonic anhydrase activity and blood lactate increases significantly (P<0.05) in diabetic when compared to normal control. However, as the course of diabetes progresses a significant (P<0.05) decrease of carbonic anhydrase activity was observed with a 2.2 fold increase in blood lactate level when compared with normal control. Treatment of diabetic rats with Acetazolamide (3.6mg/kg b.w.) resulted in 6.9 fold increase in blood lactate level and a significant(P<0.05) reduction in carbonic anhydrase activity when compared with diabetic control. Similarly treatment with Metformin (14.2 mg/kg b.w.) increased blood lactate level and reduced carbonic anhydrase activity significantly (P<0.05) when compared with diabetic control. Metformin, Acetazolamide and Methanol leaf Extract of C. farinosa were all found to have significantly(P<0.05) reduced blood glucose concentration when compared with control groups, invivo. Metformin and methanol leaf extract of C. farinosa were found to inhibit carbonic anhydrase enzyme activity in vitroagainst acetazolamide with an IC50was found to be 13.57µg/100µL. The inhibition of carbonic anhydrase activity was found to be associated with increase in glycation of hemoglobin, increase in SOD activity, decrease in the activity of catalase and a reduction in the rate of lipid peroxidation (TBARS). Fourier transform infra-red spectroscopy analysis of the inhibitor fraction of the methanol leaf extract of C. farinosa revealed a characteristic band absorption spectrum similar to aminonitrile. GC-MS analysis revealed the presence of 4-methyl-3-(2-methylhydrazino)-phenol; 2,3,4,5-tetraacetate-D-ribonitrile;           5-ethyl-2-ethylpyridine    1-oxide        derivatives     of hydrazine, ribonitrile and pyridine. The 13C NMR spectra revealed the presence of carboxylic acid moiety at dC 172.21 (C-1), OH-bonded methyl at dC 71.91 (C-3), and acetyloxy bonded to methylene adjacent to carbonyl dC 132.37 (C-6). On the basis of these findings, compound 1 was assigned as 6-acetyloxy-3-hydroxy-5-hexenoic acid.It can be concluded that inhibition of carbonic anhydrase activity reduced blood glucose concentration and may therefore be used as a possible therapeutic target for reduction of hyperglycemia in diabetes. The result indicated that C. farinosawas useful in reducing blood glucose concentration and can be used as antidiabetic medicine. The plant     may  also be a         useful      source     in         reducing      oxidative     stress.

xvii

CHAPTER ONE

1.0 INTRODUCTION

Diabetes mellitus is a metabolic disorder of impaired glucose regulation,

characterized by persistent hyperglycemia. Hyperglycemia has been associated with

increased morbidity and mortality in diabetic subjects. The development of long-

term complications in diabetes is influenced by hyperglycemia. Poor control of

hyperglycemia accelerates progression of diabetic complication.

Hyperglycemia, the major defining feature of all forms of diabetes, arises due to

absolute or relative insulin deficiency, increased hepatic glucose production (HGP),

due to increased hepatic lactate uptake produced by glycolytic cells. It has been

reported that the plasma glucose level is maintained by regulation of HGP and

glucose uptake in the peripheral tissues (DeFronzo and Ferrannini, 1987;

Cherrington et al., 1987). Moreover, fasting plasma glucose level has been shown to

be directly correlated with the rate of fasting hepatic glucose production (Bogardus