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RESEARCH LETTER
Year : 2007  |  Volume : 39  |  Issue : 5  |  Page : 253-254
 

In vitro cytotoxic and human recombinant caspase inhibitory effect of Annona reticulata leaves


1 Department of Pharmaceutical Technology, Jadavpur University, Kolkatta-700 032; Chembiotek Research International Pvt. Ltd., Block: EP&GP, Tower-B, Bengal Intelligent Park, Sector-V, Saltlake, Kolkata - 700 091, India
2 Indian Institute of Chemical Biology, Jadavpur, Kolkata -700 032, India
3 Department of Pharmaceutical Technology, Jadavpur University, Kolkatta-700 032, India

Correspondence Address:
Upal Kanti Mazumder
Department of Pharmaceutical Technology, Jadavpur University, Kolkatta-700 032
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0253-7613.37279

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How to cite this article:
Mondal SK, Mondal NB, Mazumder UK. In vitro cytotoxic and human recombinant caspase inhibitory effect of Annona reticulata leaves. Indian J Pharmacol 2007;39:253-4

How to cite this URL:
Mondal SK, Mondal NB, Mazumder UK. In vitro cytotoxic and human recombinant caspase inhibitory effect of Annona reticulata leaves. Indian J Pharmacol [serial online] 2007 [cited 2021 Oct 18];39:253-4. Available from: https://www.ijp-online.com/text.asp?2007/39/5/253/37279


Research is being carried out throughout the globe to find a lead compound which can block the development of cancer in humans. Nature has always been a great contributor towards this goal. Plant-derived natural products such as flavonoids, terpenoids and steroids have received considerable attention due to their diverse pharmacological properties, which include cytotoxic and chemopreventive effects. [1]

Caspases (cysteine-dependant aspartate specific proteases) are involved in apoptosis (programmed cell death), inflammatory responses and cellular proliferation and differentiation. The initiator and executioner caspases have gained considerable importance in drug research as caspase induction is known to have role in cancer cell death, while inhibition of caspases can be used in the therapy in acute cellular degenerative diseases such as ischemic damage and Alzheimer's disease. [2]

Annona reticulata , belonging to the family Annonaceae, is a medium-size plant found in countries with a tropical climate, such as India. The acetogenins present in the bark, fruit and leaves are known to have anticancer properties. [3],[4],[5],[6] The present study aimed to determine the in vitro cytotoxicity as well as the recombinant caspase inhibitory effect of a methanol extract of A. reticulata leaves.

The leaves of A. reticulata were collected during its fruiting season from Bangaon, West Bengal, India and identified by the Botanical Survey of India, Howrah, India. A voucher specimen (PG-212) was retained in our laboratory for further reference. The leaves were dried under shade and powdered in a mechanical grinder. The powdered material was extracted successively with petroleum ether (60-80C), chloroform and methanol, using Soxhlet apparatus. The methanol extract was concentrated in vacuo and kept in a vacuum dessicator for complete removal of the solvent. The yield was 7.5% w/w with respect to dried powder. Preliminary qualitative analysis of the methanol extract showed the presence of alkaloid, flavonoid, tannin, gum, saponins and triterpenes. The methanol extract of A. reticulata (MEAR) was used for the present study.

MEAR was dissolved in dimethyl sulfoxide (DMSO) as 25 mg/ml stock and further dilutions were made in DMSO to get lower concentrations as required for the different experiments. However, in all types of experiments, the final DMSO concentration was limited to 1%.

MEAR was investigated for cytotoxic property against Caco-2 (human colorectal adenocarcinoma), Hep G2 (human hepatocellular carcinoma) and HEK (human kidney carcinoma) cell lines, which were obtained from the National Center for Cell Sciences, Pune, India. Hep G2 and HEK cultures were maintained in DMEM at pH 7.4, supplemented with 10% heat-inactivated fetal bovine serum (PAN Biotech GmbH, Germany), ciprofloxacin 5 μg/ml and gentamycin 40 g/ml; Caco-2 was maintained with the above medium containing 10 g/ml human transferrin (Sigma, USA). The cells were grown in 25 cm 2 tissue culture flasks (Tarsons Products Pvt. Ltd, Kolkata, India), maintaining a humidified atmosphere with 5% CO 2 at 37C until confluent. The cells were dissociated with 0.2% trypsin and 0.02% EDTA in phosphate-buffered saline solution and resuspended in the respective media as stated above. Cells were plated at 20,000 cells per well in 96-well microtiter plates (Tarsons Products P Ltd, Kolkata, India) and incubated for 24 h at 37C, with 5% CO 2 in a humidified incubator. Cells were then exposed to different concentrations (20, 10, 5, 2.5, 1.25, 0.625 and 0.3125 g/ml) of MEAR in triplicate. Doxorubicin 10 M (Sigma, USA) was used as standard, while control wells received only maintenance media. Cells were incubated for 72 h and cell viability was determined using standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). [7]

For the caspase inhibition assay all the chemicals were purchased from Sigma, USA. Initiator caspase (caspase-9) and executioner caspases (caspase-3 and 6) were studied. The specific substrates were Ac-LEHD-AFC, Ac-DEVD-AFC and Ac-VEID-AFC, respectively, while the standard inhibitors were Z-LEHD-FMK, Ac-ESMD-CHO and Z-VEID-FMK, respectively.

The caspases preferentially cleave their specific substrates, resulting in release of free 4-amido-4-trifluoromethyl coumarin (AFC), which can be measured by fluorometry. [8] The reaction buffers were prepared and the analyses performed as per the enzyme manufacturer's recommended procedure. In brief, 10 ng of caspase-3, 25 ng of caspase-6 or 500 ng of caspase-9 (in the respective assay buffers) along with MEAR (5 and 10 g/ml) or the standard inhibitors (10 M) were incubated at 37C for 10 min, with shaking for allowing the extract or inhibitor to interact with the caspases. To obtain a signal-to-noise ratio at least 3 or more, different amounts of enzymes were used, as they differ in potency [2] Then the substrate solutions were added to the final concentrations of 20, 50 and 200 M, respectively, for caspases 3, 6 and 9; this was followed by incubation at 37C and shaking for 1 h. Fluorescence of free AFC was measured at excitation 370 nm and emission 480 nm. Percent caspase inhibition was calculated assuming 100% caspase activity with the wells having caspase and substrate but no inhibitor/MEAR [8] The experiments were performed thrice and the results averaged.

MEAR did not show cytotoxicity against HEK up to a concentration of 20 g/ml, while it showed good dose-dependant cytotoxicity against both Caco-2 and Hep G2 cell lines [Table - 1].

For human recombinant caspase inhibition assay, MEAR failed to show promising inhibition against caspase-3, while MEAR at 5 and 10 g/ml exhibited 56.02 and 66.64% inhibition against caspase-6 and 76.35 and 87.03% inhibition against caspase-9, respectively [Table - 2].

The results from the present study show that the extract is cytotoxic to colon and liver cancer cells and may possess anticancer activity.

Induction of caspase-3 is a common phenomenon in cancer cell death; MEAR did not show any inhibition, indicating that it has no action in preventing cancer cell death. However, marked inhibition of caspase-6 by MEAR is observed. Reports indicate that caspase-6 is effective in lamin B 1 proteolysis and keratin cleavage. But evidence for its importance in cancer cell apoptosis is lacking. [2] Caspase-6 is known to cause apoptosis in Alzheimer's disease, where its inhibition may produce a beneficial effect in such neurodegenerative diseases.

Similarly, caspase-9 inhibition may also indicate that the extract has a role in the therapy of cellular degenerative diseases. As the extract contains different type of phytochemicals it may be that the phytochemical(s) that show cytotoxicity is/are different from that which cause caspase-6/9 inhibition.

The results justify further investigation to identify the active cytotoxic principle and its inductive/inhibitory effect on different types of caspases.

 
  References Top

1.Abdullaev FI. Plant derived agents against cancer. In : Gupta SK, editor. Pharmacology and therapeutics in the new millennium. Narosa Publishing House: New Delhi, India; 2001. p. 345-54.  Back to cited text no. 1    
2.Denault JB, Salvesen GS. Caspases: Keys in the ignition of cell death. Chem Rev 2002;102:4489-500.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]
3.Yuan SS, Chang HL, Chen HW, Yeh YT, Kao YH, Lin KH, et al. Annonacin, a mono-tetrahydrofuran acetogenin, arrests cancer cells at the G1 phase and causes cytotoxicity in a Bax- and caspase-3-related pathway. Life Sci 2003;72:2853-61.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]
4.Yuan SS, Chang HL, Chen HW, Kuo FC, Liaw CC, Su JH, et al. Selective cytotoxicity of squamocin on T24 bladder cancer cells at the S-phase via Bax Bad- and caspase-3-related pathways. Life Sci 2006;78:869-74.  Back to cited text no. 4  [PUBMED]  [FULLTEXT]
5.Chang FR, Wu YC, Duh CY, Wang SK. Studies on the acetogenins of Formosan annonaceous plants. II. Cytotoxic acetogenins from Annona reticulata. J Nat Prod 1993;56:1688-94.  Back to cited text no. 5    
6.Cassady JM, Baird WM, Chang CJ. Natural products as a source of potential cancer chemotherapeutic and chemopreventive agents. J Nat Prod 1990;53:23-41.  Back to cited text no. 6  [PUBMED]  
7.Denizot F, Lang R. Rapid colourimetric assay for cell growth and survival: Modifications to the tetrazolium dye procedure giving improved sensitivity and reliability. J Immnnol Methods 1986;89:271-7.  Back to cited text no. 7    
8.Talanian RV, Quinlan C, Trautz S, Hackett MC, Mankovich JA, Banach D, et al . Substrate specificities of caspase family proteases. J Biol Chem 1997;272:9677-82.  Back to cited text no. 8  [PUBMED]  [FULLTEXT]



 
 
    Tables

  [Table - 1], [Table - 2]

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