PROMISSORY NOTE

EXHIBIT 10.15

PROMISSORY NOTE

PROMISE TO PAY. RBC Life Sciences USA, Inc. (“Borrower”) promises to pay to Independent Bank of Texas (“Lender”), or order, in lawful money of the United Stales of America, the principal amount of Five Hundred Thousand & 00/100 Dollars ($500,000.00) or so much as may be outstanding, together with interest on the unpaid outstanding principal balance of each advance, calculated as described in the “INTEREST CALCULATION METHOD” paragraph using an interest rate of 5.050% per annum based on a year of 360 days. Interest shall be calculated from the date of each advance until repayment of each advance or maturity, whichever occurs first. The interest rate may change under the terms and conditions of the “POST MATURITY RATE” section.

CHOICE OF USURY CEILING AND INTEREST RATE. The interest rate on this Note has been implemented under the “Weekly Ceiling” as referred to in Sections 303.002 and 303.003 of the Texas Finance Code. However, Lender reserves the right to implement a different interest rate and to renew such rate, provided Lender complies with the requirements of Sections 303.101, 102 and 103 of the Texas Finance Code.

PAYMENT. Borrower will pay this loan in full immediately upon Lender’s demand. If no demand is made, Borrower will pay this loan in one payment of all outstanding principal plus all accrued unpaid interest on October 22, 2009. In addition, Borrower will pay regular monthly payments of all accrued unpaid interest due as of each payment date, beginning November 22, 2008, with all subsequent interest payments to be due on the same day of each month after that. Unless otherwise agreed or required by applicable law, payments will be applied first to any accrued unpaid interest; then to principal; and then to any unpaid collection costs. Borrower will pay Lender at Lender’s address shown above or at such other place as Lender may designate in writing. Notwithstanding any other provision of this Note, Lender will not charge interest on any undisbursed loan proceeds. No scheduled payment, whether of principal or interest or both, will be due unless sufficient loan funds have been disbursed by the scheduled payment date to justify the payment.

MAXIMUM INTEREST RATE. Under no circumstances will the interest rate on this Note exceed (except for any higher default rate shown below) the lesser of 18.000% per annum or the maximum rate allowed by applicable law.

INTEREST CALCULATION METHOD. Interest on this Note is computed on a 365/360 basis; that is, by applying the ratio of the interest rate over a year of 360 days, multiplied by the outstanding principal balance, multiplied by the actual number of days the principal balance is outstanding, unless such calculation would result in a usurious rate, in which case interest shall be calculated on a per diem basis of a year of 365 or 366 days, as the case may be. All interest payable under this Note is computed using this method. This calculation method results in a higher effective interest rate than the numeric interest rate stated in this Note. (Initial here SEB)

PREPAYMENT. Borrower may pay without penalty all or a portion of the amount owed earlier than it is due. Prepayment in full shall consist of payment of the remaining unpaid principal balance together with all accrued and unpaid interest and all other amounts, costs and expenses for which Borrower is responsible under this Note or any other agreement with Lender pertaining to this loan, and in no event will Borrower ever be required to pay any unearned interest. Early payments will not, unless agreed to by Lender in writing, relieve Borrower of Borrower’s obligation to continue to make payments of accrued unpaid interest. Rather, early payments will reduce the principal balance due. Borrower agrees not to send Lender payments marked “paid in full”, “without recourse”, or similar language. If Borrower sends such a payment, Lender may accept it without losing any of Lender’s rights under this Note, and Borrower will remain obligated to pay any further amount owed to Lender. All written communications concerning disputed amounts, including any check or other payment instrument that indicates that the payment constitutes “payment in full” of the amount owed or that is tendered with other conditions or limitations or as full satisfaction of a disputed amount must be mailed or delivered to: Independent Bank of Texas, P. O. Box 167099, Irving, TX 75016-7099.

PROMISSORY NOTE

POST MATURITY RATE. The Post Maturity Rate o