When administrated orally, the vasodilating drug diltiazem can be metabolized into diacetyl diltiazem in the presence of Bacteroides thetaiotaomicron, a human gut microbe. The removal of acetyl group from the parent drug is carried out by the GDSL/SGNH-family hydrolase BT4096. Here the crystal structure of the enzyme was solved by mercury soaking and single-wavelength anomalous diffraction. The protein folds into two parts. The N-terminal part comprises the catalytic domain which is similar to other GDSL/SGNH hydrolases. The flanking C-terminal part is made up of a beta-barrel subdomain and an alpha-helical subdomain. Structural comparison shows that the catalytic domain is most akin to acetyl-xylooligosaccharide esterase and allows a plausible binding mode of diltiazem to be proposed. The beta-barrel subdomain is similar in topology to the immunoglobulin-like domains, including some carbohydrate-binding modules, of various bacterial glycoside hydrolases. Consequently, BT4096 might originally function as an oligosaccharide deacetylase with additional subdomains that could enhance substrate binding, and it acts on diltiazem just by accident.
Title: The P-glycoprotein inhibitor diltiazem-like 8-(4-chlorophenyl)-5-methyl-8-[(2Z)-pent-2-en-1-yloxy]-8H-[1,2,4]oxadiazolo[3,4-c ][1,4]thiazin-3-one inhibits esterase activity and H3 histone acetylation Cuviello F, Bisaccia F, Spinelli D, Armentano MF, Bufo SA, Cosimelli B, Ostuni A Ref: Eur Journal of Medicinal Chemistry, 164:1, 2018 : PubMed
With the aim to reduce multidrug resistance several molecules were synthesized and tested for their ability to inhibit ATP-binding cassette (ABC) proteins, which are responsible for drugs transport out from cells. The compound 8-(4-chlorophenyl)-5-methyl-8-[(2Z)-pent-2-en-1-yloxy]-8H-[1,2,4]oxadiazolo[3,4-c ][1,4]thiazin-3-one namely 2c, is structurally related to the myocardial-calcium-channel-modulator diltiazem and is considered one of the most efficient P-glycoprotein inhibitors, able to induce apoptosis at low concentrations of doxorubicin in multidrug resistant ovarian cells. In this study experiments were carried out to evaluate other biological activities of compound 2c. We verified the ability of 2c to inhibit ABC transporters do not involved in drug resistance and considering the inhibitory effect of diltiazem on recombinant human carboxylesterase, we observed its inhibitory effect on the esterase activity. Our findings demonstrated that 2c exhibits broad-spectrum activity as ABC transporters inhibitor being able to inhibit ABCC6, a protein belonging to the ABC family although poorly involved in drug resistance. 2c also inhibits cell esterase activity, acetylcholine esterase activity in vitro and cell histone H3 acetylation according to its structural homology with some known HAT inhibitors. The results obtained provide new knowledge on the biological activities of 2c and represent useful information when it is used as an inhibitor of drug resistance.
Title: Characterization of Species Differences in Tissue Diltiazem Deacetylation Identifies Ces2a as a Rat-Specific Diltiazem Deacetylase Kurokawa T, Fukami T, Nakajima M Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 43:1218, 2015 : PubMed
Diltiazem, a calcium channel blocker, is mainly metabolized via demethylation or deacetylation in humans. Diltiazem demethylation is catalyzed by cytochrome P450 2D6 and 3A4. Although it was previously reported that the area under the curve ratio of deacetyldiltiazem to diltiazem after oral dosing with diltiazem in rats was sevenfold higher than in humans, the molecular mechanisms underlying this species difference remain to be clarified. In the present study, we compared the diltiazem deacetylase activity in liver, intestinal, renal, and pulmonary microsome preparations of human and experimental animal tissues to identify the specific deacetylase enzyme(s) involved in deacetylation. Diltiazem deacetylase activity was detected in rat liver and small intestine microsome preparations, but not in those from human, monkey, dog, and mouse tissues. Further purification of rat liver microsome (RLM) proteins identified four carboxylesterase (Ces) enzymes (Ces1d, Ces1e, Ces1f, and Ces2a) as potential candidate deacetylases. On the basis of their tissue distribution, the Ces2a enzyme was considered to be the enzyme that was responsible for diltiazem deacetylation. Furthermore, recombinant rat Ces2a expressed in Sf21 cells displayed efficient diltiazem deacetylase activity with similar Km values as RLM. In addition, the inhibitory characteristics of various chemical inhibitors were similar between recombinant rat Ces2a and RLM. In conclusion, we determined that only rat tissues were able to catalyze diltiazem deacetylation. The characterization of Ces enzymes in animal species, as undertaken in this study, will prove useful to predict the species-specific pharmacokinetics differences between the in vivo models used for drug development.
Title: Protective effect of a calcium channel blocker diltiazem on aluminum chloride-induced dementia in mice Rani A, Neha, Sodhi RK, Kaur A Ref: Naunyn Schmiedebergs Arch Pharmacol, 388:1151, 2015 : PubMed
Many studies report that heavy metals such as aluminum are involved in amyloid beta aggregation and neurotoxicity. Further, high concentration of aluminum in the brain deregulates calcium signaling which contributes to synaptic dysfunction and halts neuronal communication which ultimately leads to the development of Alzheimer's disease. Recently, diltiazem, a calcium channel blocker clinically used in angina, is reported to decrease amyloid beta production by inhibiting calcium influx, decreasing inflammation and oxidative stress. However, the probable role of this drug in aluminum chloride (AlCl3)-induced experimental dementia is yet to be explored. Therefore, the present study is designed to investigate the effect of AlCl3-induced dementia in mice. Morris water maze test and elevated plus maze were utilized to evaluate learning and memory. Various biochemical estimations including brain acetylcholinesterase activity (AChE), brain total protein, thiobarbituric acid-reactive species (TBARS) level, reduced glutathione (GSH) level, nitrate/nitrite, and superoxide dismutase (SOD) were measured. AlCl3 significantly impaired learning and memory and increased brain AChE, brain total protein, TBARS, and nitrate/nitrite and decreased brain GSH or SOD. On the other hand, treatment with diltiazem significantly reversed AlCl3-induced behavioral and biochemical deficits. The present study indicates the beneficial role of diltiazem in AlCl3-induced dementia.
Title: Significantly improved expression and biochemical properties of recombinant Serratia marcescens lipase as robust biocatalyst for kinetic resolution of chiral ester Wang Y, Zhao J, Xu JH, Fan LQ, Li SX, Zhao LL, Mao XB Ref: Appl Biochem Biotechnol, 162:2387, 2010 : PubMed
A lipase gene from Serratia marcescens ECU1010 was cloned into expression vector pET28a, sequenced, and overexpressed as an N terminus His-tag fusion protein in Escherichia coli. Through the optimization of culture conditions in shake flask, the lipase activity was improved up to 1.09 x 10(5) U/l, which is a great improvement compared to our previous reports. It was purified to homogeneity by Ni-NTA affinity chromatography with an overall yield of 59.4% and a purification factor of 2.4-fold. This recombinant lipase displayed excellent stability below 30 degrees C and within the pH range of 5.0-6.8, giving temperature and pH optima at 40 degrees C and pH 9.0, respectively. The lipase activity was found to increase in the presence of metal ions such as Ca(2)+, Cu(2)+, and some nonionic surfactants such as PEG series. In addition, among p-nitrophenyl esters of fatty acids with varied chain length, the recombinant lipase showed the maximum activity on p-nitrophenyl laurate (C(1)(2)). Using racemic trans-3-(4'-methoxy-phenyl)-glycidyl methyl ester [(+/-)-MPGM] as substrate, which is a key chiral synthon for production of diltiazem, a 50% conversion yield was achieved after 4 h in toluene-water (100 mM KPB phosphate buffer, pH 7.5) biphasic system (5:5 ml) at 30 degrees C under shaking condition (160 rpm), affording (-)-MPGM in nearly 100% ee. The K(m) and V(max) values of the lipase for (+/-)-MPGM were 222 mM and 1.24 mmol min(-)(1) mg(-)(1), respectively. The above-mentioned features make the highly enantioselective lipase from Serratia marcescens ECU1010 a robust biocatalyst for practical use in large-scale production of diltiazem intermediate.
Effects of the L-type calcium channel antagonist diltiazem on recombinant human GABA(A) receptor (alpha1beta2gamma2s) or on muscle (alpha1beta1deltagamma and alpha1beta1delta(epsilon)) or neuronal (alpha7 and alpha4beta2) nicotinic acetylcholine receptors expressed in Xenopus oocytes were examined using two-electrode voltage-clamp. Diltiazem inhibited the function of both muscle and neuronal nicotinic receptors, but it had no effect on GABA(A) receptors. The extent of functional inhibition of nicotinic receptors depended on the receptor subtype, and the order of inhibition potency by diltiazem was alpha7>alpha4beta2 approximately alpha1beta1deltagamma approximately alpha1beta1delta(epsilon). Inhibition of alpha7 receptor function was non-competitive and voltage-independent, and it occurred at concentrations far lower than those needed to inhibit (never completely) binding of (125)I-alpha-bungarotoxin to heterologously expressed alpha7 receptors in mammalian cells. Pre-incubation in diltiazem before concomitant application with acetylcholine increased inhibition of function and slowed recovery from inhibition. Verapamil, a phenylalkylamine antagonist of L-type Ca(2+) channels also fully inhibited alpha7 receptor function and partially inhibited (125)I-alpha-bungarotoxin binding to alpha7 receptors, but was less potent than diltiazem. Effects on both alpha7 receptor function and (125)I-alpha-bungarotoxin binding by verapamil plus diltiazem suggest separate sites for verapamil and diltiazem on alpha7 receptors. These results provide further evidence that L-type Ca(2+) channel drugs inhibit ligand-gated cationic channels and suggest that caution should be applied when using these compounds to study systems in which L-type Ca(2+) channels and ligand-gated cationic channels co-exist.
Title: Lipases: Interfacial Enzymes with Attractive Applications Schmid RD, Verger R Ref: Angew Chem Int Ed Engl, 37:1608, 1998 : PubMed
Unusually versatile substrate specificity is shown by lipases. Not only do they hydrolyze triacylglycerols-for example, in the stomach and intestine during digestion of dietary fat-and various synthetic esters and amides, but their high stability in organic solvents permits their use in transesterification reactions and ester synthesis as well. Reactions based on lipase catalysis usually proceed with high regio- and enantioselectivity. Thus, the Ca(2+) antagonist diltiazem (1) was obtained with lipase from Serratia marcescens. Over 30 lipases have been cloned in the last few years. Since the tertiary structure of 12 lipases is known, there are presently significant efforts to improve this class of enzymes by protein engineering techniques, in view of their use in detergents and other fields of industrial application.
Title: Effect of calcium antagonists (omega-conotoxin GVIA, verapamil, gallopamil, diltiazem) on bronchial smooth muscle contractions induced by soman Walday P, Fyllingen E, Aas P Ref: Naunyn Schmiedebergs Arch Pharmacol, 346:352, 1992 : PubMed
he effect of the calcium antagonists omega-conotoxin GVIA, verapamil, gallopamil and diltiazem was investigated on in vitro bronchial smooth muscle contraction in the rat induced by the nerve agent soman. Soman inhibits the acetylcholinesterase activity irreversibly. The effect of the calcium channel antagonists on contractions induced by electrical field stimulation and carbachol was also investigated, in order to elucidate the mechanism by which calcium antagonists inhibit the soman induced contraction. omega-Conotoxin GVIA reduced the bronchial smooth muscle contraction induced by electrical field stimulation with an almost complete inhibition at approximately 1.0 x 10(-6) M. The soman induced contraction was only inhibited by 15% at a concentration of 3.0 x 10(-6) M omega-conotoxin GVIA. The organic calcium antagonists verapamil, gallopamil and diltiazem reduced both electrically and soman induced smooth muscle contraction. Complete inhibition of the contractions induced by soman was achieved at 1.4 x 10(-4) M for verapamil and gallopamil, while diltiazem inhibited the contraction to 7% of control at 1.4 x 10(-4) M. Verapamil, gallopamil and diltiazem increased the EC50 for carbachol significantly, while omega-conotoxin GVIA had no effect. None of the calcium antagonists had any effect on the maximal contraction induced by carbachol. Verapamil, gallopamil and diltiazem blocked, however, sub-maximal contractions induced by carbachol (10(-7)-10(-5) M) resulting in a right-shift of the dose response curve. The results show that omega-conotoxin GVIA inhibits the calcium-dependent release of acetylcholine which causes contraction of airway smooth muscle, while it has no effect on smooth muscle contraction induced by soman
Inhibition of the enzyme, acetylcholinesterase (AChE), at the neuromuscular junction by pyridostigmine (PYR) results in breakdown of the postjunctional folds and dissolution of the Z-discs. It is hypothesized that excess activation of the acetylcholine (ACh) receptors by unhydrolyzed ACh results in a large influx of calcium ions. This could possibly lead to the activation of calcium-dependent proteases, resulting in the observed myopathy. Pretreatment with the calcium channel blocker, diltiazem, followed by administration of both PYR and the calcium blocker resulted in a significant reduction in the extent of muscle damage due to PYR alone. In order to ascertain whether the calcium blocker could reverse the myopathy previously induced by PYR, the AChE inhibitor was administered first, resulting in significant muscle damage, followed the next day by diltiazem. After 7 days of diltiazem treatment, with continued administration of PYR, the calcium blocker significantly reduced the myopathy at the neuromuscular junction. The results are discussed in terms of possible clinical application of diltiazem in neuromuscular diseases (i.e. muscular dystrophy).
